(handbook) high performance stainless steels (11021)

8/10/2019 (Handbook) High Performance Stainless Steels (11021)

http://slidepdf.com/reader/full/handbook-high-performance-stainless-steels-11021 1/95

High-Performance

Stainless SteelsT he material presented in this reference book has beenprepared for the general information of the reader and shouldnot be used or relied upon for specific applications withoutfirst securing competent advice.

Nickel Development Institute, its members, staff, andconsultants do not represent or warrant its suitabilityfor any general or specific use and assume no liabilityor responsibility of any kind in connection with the

information herein. Drawings and/or photographs ofequipment, machinery, and products are for illustrativepurposes only, and their inclusion does not constituteor imply any endorsement of the companies thatmanufacture or distribute them.

This report was prepared by Curtis W. Kovach,Technical Marketing Resources, Inc., Pittsburgh, PA,USA, consultant to the Nickel Development Institute.

The Front Cover shows a heat exchanger withSAF 2507 ® tubes for aggressive chloride service



Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Classification of Grades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A ustenitic H igh-P erform ance S tainless S teels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Ferritic H igh-Perform ance S tainless S teels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D up lex H igh-Perform ance S tainless Steels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Physical Metallurgy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P hase R elations in the Iron-C hrom ium -N ickel S ystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .S econdary P hases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1K inetics of P hase P recipitation R eactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1A ustenitic S tainless S teels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Ferritic S tainless S teels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1D uplex S tainless S teels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2A ustenitic S tainless S teels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Ferritic S tainless S teels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2D uplex S tainless S teels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Physical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Corrosion Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3R esistance to Inorganic A cids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3R esistance to O rganic A cids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4R esistance to A lkalies and A lkaline S alts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4C hloride- and O ther H alide Ion-C ontaining A queous Environm ents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4N ear N eutral Environm ents –N atural W aters and B rines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Influence of M icrobial A ctivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5O xidizing H alide E nvironm ents –C hlorinated C ooling W aters and B leach S olutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5A cidic E nvironm ents C ontaining H alides –Flue G as C ond ensates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Stress Corrosion Cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6W ater and B rine Environm ents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6S our O il and G as Environm ents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6H ydrogen E nvironm ents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Corrosion Acceptance Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

TABLE OF CONTENTS



Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7H ot W orking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7C old W orking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7A nnealing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Machining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7A ustenitic S tainless S teel G rad es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Ferritic S tainless S teel G rades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7D up lex S tainless S teel G rad es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Surface Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Works Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Appendix 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Appendix 2 (A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Appendix 2 (B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Appendix 2 (C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Appendix 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Appendix 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

TABLE OF CONTENTS (continued)


http://slidepdf.com/reader/full/handbook-high-performance-stainless-steels-11021 4/95 High-Performance Stainless Steels•3

as individual grades, m ay offer optim umperform ance for a sp ecific req uirem ent. The

higher nickel austenitic grades are generally

preferred for severe acid service and forresistance to chloride pitting and stress corrosion

cracking. They are often selected for flue gascleaning eq uipm ent hand ling acid cond ensates,

or acidic solutions containing strong oxidantssuch as in pap er bleaching . W here field

fabrication is an im portant consideration, theausten itic grad es are favoured because o f their

relative ease of w elding; grades from this fam ilyhave b een used extensively in offshore and

nuclear piping w here w eld quality is extrem elyim portant. If the requirem ent is for thin sheet, the

ferritic grades w ill usually be m ost cost-effective;

therefore, they have been used as the tub em aterial in m any kind s of heat exchang ers. The

duplex g rad es are o ften selected w here strengthis advantageous. They have been used in

pressure vessels for the chem ical processindustry, and have seen extensive service in heat

exchangers. A ll three fam ilies o f the high-perform ance stainless steels w ill deliver a w ide

range of resistance to chloride pitting and stresscorrosion cracking superior to that

of Types 304 and 316; so fab rication

considerations often d eterm ine the final m aterial

choice in the case of chloride service .

The high-perform ance stainless steels are m ore

technically dem anding than Types 304 and 31 6w ith regard to m etallurgy and fabrication

req uirem ents. This is due to the nature ofthe steels them selves and the dem and ing

ap plications in w hich they are used. A tho roughunderstanding of these stainless steels is

necessary to use them successfully. This book

provides assistance in m aking the optim umm aterial selection for a g iven application, and

provides guidance in the fab rication and use ofthe selected grade. B ecause of the com plexity of

applications and large num ber of grad esavailab le, this book can serve only as an

introductory guide. The reader is encourag ed toco nsult w ith m anufacturers to learn m ore fully the

advantages, lim itations, and sp ecificrequirem ents of individual m aterials.

INTRODUCTIONThe “high-perform ance stainless steels”are a

fam ily of stainless steels w hich have distinctlysuperior corrosion resistance in a w ide variety of

aggressive environm ents w hen com pared w ith thestandard stainless steel grad es such as Typ e*

304L, w hich contains only 18% chrom ium and8% nickel (18-8), and Type 316L, w hich contains

sim ilar chrom ium and nickel and 2% m olybdenum(18-10-2). Their superiority in resisting pitting and

stress corrosion cracking is especially evident inenvironm ents containing the chloride ion. This

perform ance is obtained by using a high level ofchrom ium , nickel, m olybd enum , and nitrog en

alloying for co rrosion resistance, and by p roducing

these g rades w ith very low carbon contents topreserve this resistance w hile allow ing hot

fab rication and w elding. The com m ercial origins ofthe high-perform ance stainless steels cam e w ith

the advent of steel m elting and refiningtechnologies that m ade it possible to

econo m ically produce com positions having verylow carbon content and close com position

control. A m ong these technologies are vacuumm elting, electron beam rem elting, electroslag

rem elting , and, m ost no tab ly today from acom m ercial stand po int, vacuum oxygen

decarburization (VO D ) and argon-oxygendecarburization (A O D ). B eg inning in the 1970s,these stainless steels have grow n in num ber and

in technical and com m ercial im portance. Thisbook provides an introduction to these steels for

those w hose m aterials needs extend beyond thecapab ilities of the standard grad es, and for those

w ho w ill benefit from a discussion of theengineering and corrosion perform ance p roperties

of the high-perform ance stainless steels.

There are three prim ary classifications w ithin thehigh-perform ance stainless steels. They are the

austenitic, ferritic, and duplex (austenitic-ferritic)

fam ilies. The stainless steels in each fam ily havegeneral sim ilarities, but there is also a w ide range

of corrosion resistance and other characteristics.This allow s a broad spectrum of existing and

poten tial ap plications w here each fam ily, as w ell

* R efers to ‘A IS ITyp e’.


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CLASSIFICATIONOF GRADES

AUSTENITICHIGH-PERFORMANCESTAINLESS STEELSThe austenitic fam ily of high-perform ance

stainless steels shares m any characteristics w ithits standard grad e counterpart. These g rad es in

the annealed condition co nsist prim arily of asingle p hase, face-centred cubic austenite,

and are non-m agnetic. This structure is

characterized by a relatively low yield strength,high w ork hardening rate and high tensile

strength, good ductility and form ability,esp ecially good low tem perature toug hness, and

the inability to be hardened (or strengthened) by

heat treatm ent. B esides corrosion resistance,the m ajor difference in com parison w ith the

standard g rad es is that the high-perform ancegrad es rap idly form second ary phases at high

tem peratures. These phases m ay be d am agingto certain m echanical properties and corrosion

resistance, and therefore, the application ofthese stainless steels at tem peratures ab ove

500°C (930°F) is lim ited. In addition, care m ustbe taken to avoid form ing dam aging am ounts

of these p hases d uring high tem perature

operations such as forging o r w elding.

A list of no tab le w rought high-perform anceausten itic stainless steels is g iven in Table 1 .

G rades are identified by the nam e b y w hichthey are best know n and b y their U N S num ber.

P rod ucer nam es, w hich in m any cases are



trade nam es, are p rovided in A ppendix 2. M any

of these grad es w ere p atented w hen originallydevelop ed and, in som e cases, the p atents

m ay still be in effect. W hen a range is show nfor the chem ical co m position, it corresponds to

the m ost com m only applicab le A S TM stand ard,usually A 240. W hen sing le com positions are

show n, this is the “typ ical”value providedby the producer. The grad es in Table 1are arranged in the order of increasingm olybdenum , chrom ium , and nitrogen content,

or increasing P R E num ber. The P R E num berm eans the “pitting resistance equivalent”and in

this book is defined as PR E = % C r + 3.3% M o

+ 16 % N w ith the p ercent elem ents in w eight

percent. A higher P R E num ber relates sem i-

quantitatively to a higher resistance to localizedco rrosion in ch loride-containing environm ents.

The grad es a lso have been d ivided into sixsubgroups b ased on a sim ilarity in localized

corrosion resistance. A description of thesesub group s follow s:

Subgroup A-1 Austenitic Stainless Steels.The stainless steels in this subgroup aredesigned prim arily for application in strong,

hot, sulphuric acid so lutions. The requiredcorrosion resistance is achieved prim arily

throug h the use of high nickel co ntent. The

20 C b-3 and A lloy 825 grades, w ith about the

Table 1 Chemical composition* of wrought high-performance austenitic stainless steels (wt. pct.)**

UNS Sub PREName Number Group C N Cr Ni Mo Cu Other Numb

Type 316L S31603 0.03 0.10 16.0-18.0 10.0-14.0 2.0-3.0 – – 23Type 317L S31703 0.03 0.10 18.0-20.0 11.0-15.0 3.0-4.0 – – 28

Alloy 20 N08020 0.07 – 19.0-21.0 32.0-38.0 2.0-3.0 3.00-4.00 (Cb+Ta): 8xC-1.00 26 A-1

Alloy 825 N08825 0.05 – 19.5-23.5 38.0-46.0 2.5-3.5 1.50-3.50 Al: 0.2 max, Ti: 0.6-1.2 28317LN S31753 0.03 0.10-0.22 18.0-20.0 11.0-15.0 3.0-4.0 – – 30260 0.03 0.16-0.24 18.5-21.5 13.5-16.5 2.5-3.5 1.00-2.00 – 29

A-2317LM S31725 0.03 0.10 18.0-20.0 13.2-17.5 4.0-5.0 – – 31317LMN S31726 0.03 0.10-0.20 17.0-20.0 13.5-17.5 4.0-5.0 – – 32NAS 204X*** 0.04 – 25.0 25.0 2.75 – Nb: 10xC 34310MoLN S31050 0.03 0.10-0.16 24.0-26.0 21.0-23.0 2.0-3.0 – Si: 0.50 max 32700 N08700 0.04 – 19.0-23.0 24.0-26.0 4.3-5.0 – Nb: 8xC-0.40 33904L N08904 0.02 – 19.0-23.0 23.0-28.0 4.0-5.0 1.00-2.00 – 32

A-3904LN 0.02 0.04-0.15 19.9-21.0 24.0-26.0 4.0-5.0 1.00-2.00 3420Mo-4 N08024 0.03 – 22.5-25.0 35.0-40.0 3.5-5.0 0.50-1.50 – 3420 Mod N08320 0.05 – 21.0-23.0 25.0-27.0 4.0-6.0 – Ti: 4xC min 34

Alloy 28 N08028 0.02 – 26.0-28.0 29.5-32.5 3.0-4.0 0.60-1.40 – 3620Mo-6 N08026 0.03 0.10-0.16 22.0-26.0 33.0-37.0 5.0-6.7 2.00-4.00 – 4025-6MO N08925 0.02 0.10-0.20 19.0-21.0 24.0-26.0 6.0-7.5 0.8-1.5 – –

1925hMo254N*** 0.03 0.20 23.0 25.0 5.50 – – 4125-6MO N08926 A-4 0.02 0.15-0.25 19.0-21.0 24.0-26.0 6.0-7.0 0.50-1.50 – 411925hMoSB8 N08932 0.020 0.17-0.25 24.0-26.0 24.0-26.0 4.7-5.7 1.0-2.0 – 42254 SMO S31254 0.02 0.18-0.22 19.5-20.5 17.5-18.5 6.0-6.5 0.50-1.00 – 42

AL-6XN N08367 0.03 0.18-0.25 20.0-22.0 23.5-25.5 6.0-7.0 0.75 – 43 YUS 170 0.03 0.25-0.40 23.0-26.0 12.0-16.0 0.50-1.20 – – 292419 MoN A-5 0.03 0.30-0.50 23.0-25.0 16.0-18.0 3.5-4.5 0.30-1.00 Mn: 5.5-6.5

Nb: 0.1-0.3 394565S S34565 0.03 0.40-0.60 23.0-25.0 16.0-18.0 3.5-5.0 – Mn: 3.5-6.5 41B66 S31266 0.030 0.35-0.60 23.0-25.0 21.0-24.0 5.0-7.0 0.50-3.00 W: 1.0-3.0

Mn: 2.00-4.00 453127 hMo N08031 A-6 0.02 0.15-0.25 26.0-28.0 30.0-32.0 6.0-7.0 1.00-1.40 – 48654 SMO S32654 0.02 0.45-0.55 24.0-26.0 21.0-23.0 7.0-8.0 0.30-0.60 Mn: 2.0-4.0 54

Cu: 0.3-0.6

AL-6XN ®

flexible hosing

for offshore

oil rigs


http://slidepdf.com/reader/full/handbook-high-performance-stainless-steels-11021 7/956•High-Performance Stainless SteelsSubgroup A-2 Austenitc rStainless Steels.These grades, for ex



Group A-6 Austenitic Stainless Steels.These grades, for exam ple 654 S M O ,

rep resent the h ighest level of perform ancethat has yet been achieved am ong all the

high-perform ance stainless steels. Theycom bine high strength w ith outstanding

localized co rrosion resistance, and havegood chloride stress corrosion cracking and

acid resistance. They w ill resist stresscorrosion cracking in the boiling 45% M gC l 2

test and localized co rrosion in seaw ater

und er severe crevice co nd itions andtem peratures significantly ab ove am bien t.

They ap proach the best of the nickel-basealloys w ith respect to localized corrosion

w hile p roviding m uch higher strength. Thesenew er grad es have an excellent potential for

solving crevice co rrosion problem s in

gasketed joints, system s handling seaw aterat elevated tem peratures, and in m anysystem s operating at high p ressure.

FERRITIC HIGH-PERFORMANCESTAINLESS STEELSThe ferritic high-perform ance stainless steels

have an entirely ferritic m icrostructure exceptfor sm all am ounts o f stab ilizing carbides and

nitrides. This ferritic structure has the uniqueattribute of being very resistant to chloride

stress corrosion cracking, but has lim itedtoughness. The toughness can be further

reduced by large section o r grain size effectsand by the precipitation of em brittling

second ary phases. These grad es are usuallyno t produced in p late thicknesses b ecause of

these toughness lim itations. They w ere

developed to p rovide superior resistance,co m pared to the 18-8 stainless steels, to

chloride stress corrosion cracking and pitting ata low er cost than the high nickel-co ntaining

austenitic alloys. They are generally used onlyfor heat exchanger tubing or thin sheet

ap plications. They are not hardenab le b y heattreatm ent, but in the annealed co ndition they

exhibit higher strength than m any austeniticgrades. Table 2 lists the notable w rought ferritic

grades in order of increasing resistance to

chloride pitting.

Subgroup F-1 Ferritic Stainless Steels.These grades, for exam ple E-B R ITE 26 -1,

have localized corrosion resistance sim ilar toType 316, but far superior stress corrosion

cracking resistance. This good stress

corrosion cracking perform ance ap plies tohot, co ncentrated caustic as w ell as ch loride-containing solutions.

Subgroup F-2 Ferritic Stainless Steels.The grad es in this subgroup, w hich include

S EA -C U R E, w ere designed to resistlocalized co rrosion in am bient tem perature

seaw ater. They have been used extensivelyin seaw ater-cooled pow er plant cond ensers.

W ith their high chrom ium content andm od erate m olybdenum and nickel content,

they are also very resistant to strong organicacids and oxidizing or m oderately red ucing

inorganic acids. H ow ever, the use of nickelin m any of these grad es reduces chloride

stress co rrosion cracking resistance andincreases susceptibility to the form ation of

dam ag ing seco ndary phases. A ll these ferritic

Name UNS Number Sub Group C N Cr Ni Mo Cu Other PRE Number

Type 444 S44400 0.025 0.035 17.5-19.5 1.00 1.75-2.50 – Ti, Nb 2326-1S S44626 F - 1 0.060 0.040 25.0-27.0 0.50 0.75-1.50 – Ti 27E-BRITE 26-1 S44627 0.010 0.015 25.0-27.0 0.50 0.75-1.50 – Nb 27MONIT S44635 0.025 0.035 24.5-26.0 3.5-4.5 3.5-4.5 – Ti, Nb 36SEA-CURE S44660 F - 2 0.030 0.040 25.0-28.0 1.0-3.5 3.0-4.0 – Ti, Nb 35

AL 29-4C S44735 0.030 0.045 28.0-30.0 1.00 3.6-4.2 – Ti, Nb 40 AL 29-4-2 S44800 F-3 0.010 0.020 28.0-30.0 2.0-2.5 3.5-4.2 – – 40

Table 2 Chemical composition* of wrought high-performance ferritic stainless steels (wt. pct.)**



stainless steels resist stress corrosioncracking in sodium chloride tests, butprobab ly not in the m agnesium chloride test

because of their nickel co nten t (0.5-4.2% ).

Subgroup F-3 Ferritic Stainless Steels.The o ne grade in this sub group, A L 29 -4-2,as w ith the A -6 austen itic subgroup, is

designed to produce the highest level ofoverall perform ance available from the ferritic

stainless steels. It com bines good localizedand acid co rrosion resistance.

DUPLEX HIGH-PERFORMANCESTAINLESS STEELSThe grad es in the duplex fam ily are

m etallurgically d esigned to have a

m icrostructure in the annealed co nditionco nsisting of ap proxim ately eq ual portions of

austenite and ferrite. This is achieved by lim iting

the nickel co ntent to m oderately low levels andincreasing the chrom ium content up to 2 2-26% . The m olybdenum con tent is kept to

ab out the sam e level as 317L. Therefore, w henthe P R E num bers are higher than ab ou t 30 , as

for 317L, it is m ostly a result of the h igherchrom ium and nitrog en contents. The d up lex

structure exhibits p roperties that takead vantage o f the b etter attributes of each of

the tw o phases. M ost im portantly, these grad es

provide very high strength along w ith usefulductility and toughness. They can deliver agood com bination of strength, general

corrosion, and stress corrosion cracking

resistance at m od erate cost because they donot co ntain a large am ount of nickel. A s w ith

the austenitic fam ily, these grades cannot behardened by heat treatm ent. D up lex stainless

steels require careful fabrication procedures toavoid dam age from secondary phases and to

m aintain the b alance o f ab out equal am ounts offerrite and austenite. They are m ore d em anding

than the austen itic stainless steels in thisresp ect. Table 3 lists the notab le w rought high-

perform ance duplex stainless steels.

Subgroup D-1 Duplex Stainless Steels.The only grade in this subgroup is 2304.A lthough it generally does not have b etter

co rrosion resistance than the standard

austenitic grad es, 2304 is includ ed am ongthe high-perform ance stainless steelsbecause, as w ith all the second generation

dup lex grades, it uses low carbon and highnitrogen to give a better com bination o f

fabrication and corrosion p roperties than theearlier duplex grades. It can be readily

w elded and offers higher strength and betterstress corrosion cracking resistance than

Type 31 6L o r Type 3 17L.

Subgroup D-2Duplex StainlessSteels.The g rad es in this

subgroup, especially

2205 , are the m ostuseful of the duplexfam ily because they

com bine corrosionperform ance, ease of

fabrication andecono m ical properties.

They have greatversatility in both

fabrication and

Table 3 Chemical composition* of wrought high-performance duplex stainless steels (wt. pct.)**

Name UNS Number Sub Group C N Cr Ni Mo Cu Other PRE Num

Type 329 S32900 0.080 – 23.0-28.0 2.5-5.0 1.00-2.00 – – 263RE60 S31500 0.030 0.05-0.10 18.0-19.0 4.25-5.25 2.50-3.00 – Si: 1.40-2.00 Mn:1.20-2.00 272304 S32304 D - 1 0.030 0.05-0.20 21.5-24.5 3.0-5.5 0.05-0.60 – – 2245M*** 0.030 0.15 24.3 5.0 1.50 1.00 – 3244LN S31200 0.030 0.14-0.20 24.0-26.0 5.5-6.5 1.20-2.00 – – 302205 S31803 D - 2 0.030 0.08-0.20 21.0-23.0 4.5-6.5 2.5-3.5 – – 312205 S32205 0.030 0.14-0.20 22.0-23.0 4.5-6.5 3.0-3.5 – – 347-Mo PLUS S32950 0.030 0.15-0.35 26.0-29.0 3.5-5.2 1.00-2.50 – – 32DP3 S31260 0.030 0.10-0.30 24.0-26.0 5.5-7.5 2.5-3.5 0.20-0.80 W: 0.10-0.50 34UR 47N D - 3 0.030 0.14-0.20 24.0-26.0 5.5-7.5 2.5-3.5 – – 3464*** 0.030 0.14 25.0 6.40 3.5 – – 39255 S32550 0.040 0.10-0.25 24.0-27.0 4.5-6.5 2.9-3.9 1.50-2.50 – 35DP3W S39274 0.030 0.24-0.32 24.0-26.0 6.0-8.0 2.5-3.5 0.20-0.80 W: 1.50-2.50 36100 S32760 0.030 0.20-0.30 24.0-26.0 6.0-8.0 3.0-4.0 0.50-1.00 W: 0.50-1.00 372507 S32750 D - 4 0.030 0.24-0.32 24.0-26.0 6.0-8.0 3.0-5.0 0.50 – 3852N+ S32520 0.030 0.20-0.35 24.0-26.0 5.5-8.0 3.0-5.0 0.50-3.00 – 37



corrosion resistance.

They are superior toType 316 in resistance

to stress corrosioncracking.

Subgroup D-3Duplex StainlessSteels.These 25C r duplex

grades, such asFerralium 255, use

higher levels ofchrom ium to p rod uce

better localizedcorrosion resistance

than the subgroup D -2grad es, but they are

PHYSICALMETALLURGY

PHASE RELATIONS IN THEIRON-CHROMIUM-NICKELSYSTEM

The high-perform ance stainless steels are best

understood m etallurgically by exam ining theiron-chrom ium -nickel ternary system and

co nsidering m odifications introduced by otheralloying elem ents. This ternary system usefully

delineates the tw o p rim ary phases, austen iteand ferrite, w hich distinguish the three

structural fam ilies. The p rim ary additional

elem ents are m olybd enum , nitrog en, andcarbon, and, in the case of stabilized ferritic

stainless steels, titan ium and niobium . Theseelem ents, along w ith chrom ium , introduce

secondary phases that are usually und esirab le.A good understanding of the cond itions o f

occurrence and effects of the p rim ary andsecondary phases is essential to the successful

use of the high-perform ance stainless steels.

A section of the iron-chrom ium -nickel systemat 1100 °C (20 12 °F) is show n in Figure 1 .

This section provides a reasonably good

rep resentation of the p rim ary phaserelationships for all these grades at

tem peratures from about 100 0°C (18 32 °F) to

near their so lidus tem peratures. In this diagramthe region of m ost interest is that w hichencom passes iron contents of about 50 to 70

percent and chrom ium contents (plusm olybdenum ) of about 20 to 30 p ercent. The

shaded regions of Figure 1 show the generalcom position range for the three alloy fam ilies:

austenitic totally w ithin the gam m a field ( γ ),ferritic totally w ithin the alpha field ( α ), and

dup lex w ithin the alpha plus gam m a field ( α +

not co nsidered to be seaw ater-resistan t incritical applications. The chrom ium provides

very good resistance to oxidizing acids. Theyreq uire higher nickel to balance the higher

chrom ium , w hich im proves resistance tored ucing acids as w ell. The high chrom ium

has the disad vantage of accelerating thekinetics of dam aging detrim ental phase

precipitation; therefore, fabrication invo lvingtherm al treatm ent req uires close control of

therm al conditions. The rapid precipitation

kinetics in som e instances m ay lim it usablesection sizes.

Subgroup D-4 Duplex Stainless Steels.This subgroup is the m ost highly alloyedsubgroup of the duplex fam ily. The h igh

chrom ium , m olybdenum , nickel, and nitrogen

content produces the best co rrosionresistance of any of the duplex grad es, andhigher strength than is obtainable in any

high-perform ance stainless steel. For thisreason, these alloys are so m etim es called

super duplex stainless steels. Resistance to

pitting and crevice co rrosion in am bien ttem perature seaw ater is sim ilar to the 6 %

M o austenitic g rades in S ub group A -4. They

have yield strengths exceed ing 550 M P a (80ksi). H ow ever, their high alloy contents

produce restraints on therm al fabricatingprocedures that are even m ore stringent than

req uired for the sub group D -3 grades.

Figure 1 Section of the iron-chromium-nickel system at 1100°C (2012°F) showingthe general composition range of ferritic, duplex and austenitic high-

performance stainless steels 1

Cr

Fe Ni10 20 30 40 50 60 70 80 90

High-Performance Austenitic

High-Performance Ferritic

High-Performance Duplex

γ

α+γ

α

9 0

8 0

7 0

6 0

5 0

4 0

3 0

2 0

1 0 9 0

8 0

7 0

6 0

5 0

4 0

3 0

2 0

1 0



This section indicates

relatively sim ple o ne- ortw o-phase alloys and

generally applies at high

tem perature for thecom m ercial grades eventhough they w ill contain

additional alloying orresidual elem ent

com po nents. Thedetrim ental secondary

phases m entioned

previously are stableonly at tem peratures

less than abou t 10 00 °C(1832 °F). The successful

com m ercial production of the high-perform ance stainless steels, and their

fabrication and use, require a relatively sim ple

m icrostructure and avo idance of detrim entalsecond ary phases d uring exposure to low er

tem peratures up on cooling after annealing orw elding .

S igm a p hase is the m ost often encountered

second ary phase and it is often dam aging toboth m echanical properties and corrosion

resistance. U nder equilibrium conditions sigm acan form at interm ed iate tem peratures in

virtually all these alloys. This is illustrated in

Figure 2 , a section o f the iron-chrom ium -nickel

ternary at 650°C (1202°F). From this section, it

can be seen that large q uantities of sigm a canoccur in the higher chrom ium ferritic and

duplex grad es, and in m ost of the austeniticgrad es as w ell. B ecause diffusion rates are

faster in ferrite than in austenite, reactionkinetics also favour sigm a form ation in those

co m positions w hich contain ferrite. S igm aphase is p articularly d am aging to toug hness in

Figure 2 Section of the iron-chromium-nickel system at 650°C (1202°F) showing the stability of sigma phase existing over the composition range of many high-

performance stainless steels 1

Cr

Fe Ni

γ

α+γ

γ+σ

α+σ

α+γ

σ

α

α

α+σ

AL-6XN ® stainless steel

wallpaper for flue gas

desulphurization

ductwork

10 20 30 40 50 60 70 80 90

9 0

8 0

7 0

6 0

5 0

4 0

3 0

2 0

1 0 9 0

8 0

7 0

6 0

5 0

4 0

3 0

2 0

1 0



the ferrite-containing grades, but also adversely

affects toug hness and corrosion effects w henpresent in austenite.

The iron-chrom ium binary phase d iagram

show n in Figure 3 provides a good description

of phase relationships in the com m ercial high-perform ance ferritic stainless steels. W hen

carbon and nitrogen are stabilized w ith titaniumand niobium , the position o f the gam m a loop is

abou t as show n in the d iagram and thesecom positions structurally w ill consist entirely of

ferrite at chrom ium levels ab ove about 11% .In the norm al solution annealed co ndition,

particles of titanium and niobium carbonitridew ill occur random ly throughout the ferrite

m atrix. S igm a phase can form in these alloysat chrom ium contents above about 20% and

at even low er chrom ium con tents w hen

m olybd enum is present.

Evidence of alpha prim e form ation has beendetected at chrom ium contents as low as 12 %

in com m ercial alloys containing titanium afterprolonged service exp osures at elevated

tem perature. A lpha prim e w ill form rap idly at

ferrite chrom ium contents above about 18% .

M olybdenum and other alloying elem ents w illaffect the stability ranges and the kinetics of

form ation of these and other second aryphases, generally prom oting their form ation.

From the standpoint of the com m ercial

production and ap plication of these stainlesssteels, practices are alw ays d esigned to

m aintain a ferritic structure containing onlytitan ium or niobium carbonitrides. A review by

J. J. D em o and other excellent papers found in“S ource B ook on Ferritic S tainless S teels”,

ed ited by R . A . Lula 3 provide a detaileddiscussion on the m etallurgy of the ferritic

stainless steels.

P seud o-binary sections through the iron-chrom ium -nickel ternary help illustrate the

effect of tem perature on reg ions o f phase

stability for the duplex and austenitic alloys. Forthe duplex stainless steels, a section through

the ternary at 60% iron as proposed byPugh ( Figure 4 ) is useful. D uplex alloys

characteristically solidify as ferrite. Increasingam ounts of austenite then beco m e stab le at

low er tem peratures to abou t 10 00 °C (18 32 °F).

Figure 4 Section through the Fe-Cr-Ni ternary phase diagram at 60% iron showingthe effect of small changes in nickel

and chromium on the ferrite and austenite in duplex stainless steels 4

0 5 10 15 20 25 30 35 40

T e m p e r a t u r e (

˚ C )

Nickel (weight%)

1600

1400

1200

1000

800

600

400

200

0

2912

2552

2192

1832

1472

1112

752

392

32

α+L γ +L

γ

α+σ

α+γ

α+γ+σ

α

Figure 3 Iron-chromium phase diagram showing the stability of sigma ( σ ) and alpha prime ( α ) phases over a broad chromium range at low temperature 1,2

0 10 20 30 40 50 60 70 80 90 100

T e m p e r a t u r e

( ˚ C )

T em p

er a t ur e ( ˚ F )

Chromium (weight %)

2000

1800

1600

1400

12001000

800

600

400

200

0

3632

3272

2912

2552

21921832

1472

1112

752

392

32

α

α+L

L

γ

α ´ α´

α+γ

σ

α α

α+L

L



The relative am ounts of ferrite and austeniteare critically dep endent on the chem ical

co m position and its therm al history. S m allchanges in com position o r therm al treatm ent

can have large effects on the relative volum efraction of these tw o phases in a finished m ill

prod uct or com ponent after a therm altreatm ent such as w elding . P hase d iagram s

have no t been develop ed to take into accountthe m any elem ents that influence p hase

balance in the d uplex alloys. H ow ever, therelative phase-form ing tendencies of specific

elem ents as they are know n for the austenitic

grades w ill also apply reasonably w ell to theduplex grad es. B ecause ferrite is the prim ary

so lidification phase, it is p ossible to have m orethan the equilibrium am ount of ferrite in a

finished m ill product after fabrication, but theopposite is not true w ith resp ect to austenite.

S igm a phase is also a stab le p hase in the high-

perform ance dup lex stainless steels as show nin Figure 4 . The up per tem perature lim it of

sigm a phase stab ility is som ew hat higher in theduplex g rades than it is in the ferritic grades,

approaching about 90 0°C (16 52 °F). A lpha

prim e also can precipitate in duplex alloys,form ing in the ferrite phase in the sam e m anner

as occurs in the fully ferritic alloys. The use ofnitrogen as an alloying elem ent in these

stainless steels can result in chrom ium nitridesalso being present, especially w hen the ferrite

co ntent is high.

Tem perature-dependent phase relations for theaustenitic stainless steels are illustrated in

Figures 5 and 6 w ith pseud o-binary sectionsthroug h the Fe-C r-N i ternary at 16% and 2 0%

nickel. D ep ending on com position, these alloyscan solidify w ith austen ite phase as the prim arydendrites or in a m ixed m ode of ferrite and

austenite. Because austenite grain boundariesare m ore susceptible to im purity-related

phenom ena than ferrite or austenite-ferritebound aries, and because diffusion rates are

generally less in austenite, there can beco nsiderable differences in hot cracking, hot

w orking , and segregation behaviour am ong the

Figure 6 Section through the Fe-Cr-Ni ternary phase diagram at 20% nickel showingthe solidification mode with respect to

austenite and ferrite in austenitic stainless steels 5

0 10 20 30 40 50 60 70 80


( ˚ C )

T em p er a t ur e ( ˚ F )

Chromium (weight %)

2000

1800

1600

1400

1200

1000

800

600

400

200

0

3632

3272

2912

2552

2192

1832

1472

1112

752

392

32

α

δ+α

L

γ

α+γ+σ

α+γ

δ+α+γ δ+γ

α+γ

γ+σ

Figure 5 Section through the Fe-Cr-Ni ternary phase diagram at 16% nickel showingthe solidification mode with respect to

austenite and ferrite in austenitic stainless steels 5

0 10 20 30 40 50 60 70 80


( ˚ C )


Chromium (weight%)

2000

1800

1600

1400

1200

1000

800

600

400

200

0

3632

3272

2912

2552

2192

1832

1472

1112

752

392

32

αδ+α

L

γ

α+γ+σ

α+γ

δ+α+γ δ+γ

α+γ

γ+σ



ferrite existing below the solidus tem perature,

especially in the low er nickel grad es as show n in

Figure 5 . As w ith the other stainless steel fam ilies,

sigm a and other secondary phases becom estable at low er tem perature. The upper

tem perature lim it of sigm a p hase stability in thecom m ercial grades is about 1050°C (1922°F),

higher than in the ferritic or duplex grades. Theextent to w hich these p hases m ay occur

depends on actual chem istry, solidification rate,

segregation effects, and therm al-m echanicaltreatm ents. The occurrence of at least a sm all

am ount of one or m ore of these p hases shouldbe considered typical in m any of the com m ercial

austenitic grades.

SECONDARY PHASES

Sim ple ternary phase diagram s provide only astarting point for understanding the com plex

m etallurgy of these m ulti-com ponent alloys. It isalso im portant to know w hat secondary phases

can exist and under w hat circum stances,because their occurrence can have p rofound

effects on corrosion resistance and m echanical

prop erties. Secondary phases that have beenfound in the high-perform ance stainless steels are

listed in Table 4 . They can be classified as eithercarbides, nitrides, or interm etallic com pounds.

various high-perform anceausten itic stainless steels

depend ing on their m od e

of solidification.C om positions w hich

produce som e ferrite atthe tim e of solidification

are less susceptible toso lidification and other

ho t cracking problem s.D epending on

com position, there is thepossibility o f equilibrium

Table 4 Secondary phases in high-performance stainless steels

Stainless Phase Symbol Type Formula Temperature Structure LatticeSteel* Range Constants

D chromium – M7C3 (Cr,Fe,Mo)7C3 950-1050°C orthorhombic a=4.52, b=6.99,carbide c=12.11

A, D, F chromium – M23C6 (Cr,Fe,Mo)23C6 600-950°C cubic a=10.57-10.68carbide

A, D, F chromium – M6C (Cr,Fe,Mo,Cb)6C 700-950°C cubic a= 10.93-11.28carbide

D, F chromium – M2N (Cr,Fe)2N 650-950°C hexagonal a=2.77, c=4.46nitride

D chromium – MN CrN – cubic –nitride

D Fe-Mo – M5N Fe7Mo13N4 550-600°C – a = 6.47nitride

A Nb-Cr Ζ MN (NbCr)N 700-1000°C tetragonal a=3.03, c=7.37nitride

F titanium – MC Ti(CN) 700°C-m.p. cubic a=4.32-4.24carbo-nitride

F niobium – MC Nb(CN) 700°C-m.p. cubic a=4.42-4.38carbo-nitride

A, D, F Sigma σ AB (Fe,Cr,Mo,Ni) 550-1050°C tetragonal a=8.79, c=4.54

A, D, F Chi χ A 48B10 Fe36Cr12Mo10 600-900°C cubic a=8.86-8.92(FeNi)36Cr18(TiMo)4

D, F Alpha prime α´ - CrFe(Cr 61-83%) 350-550°C cubic a=2.877

A, D, F Laves η A 2B (FeCr)2(Mo,Nb,Ti,Si) 550-900°C hexagonal a=4.73-4.82, c=7.26-7.85

D, F R R – (Fe,Mo,Cr,Ni) 550-650°C rhombohedral a=10.903, c=19.347

D Tau τ – – 550-650°C orthorhombic a=4.05, b=4.84, c=2.86



precipitates form ed at interm ediate

tem peratures by inadeq uately rap id coolingfrom the annealing tem perature range o r

upon co oling after w elding. O f the variouspossible chrom ium carbides, the M 23 C6 type

is b y far the m ost co m m on. It w ill usuallycontain som e m olybdenum , and generally

precipitates over the 550-950°C (1020°F-

1740°F) tem perature range. O ther carbidesthat have b een reported are the M 7C3 and

M6C types as described in Table 4 .Intergranularly precipitated carbides can

produce intergranular corrosion and alsoreduce the pitting resistance. These effects

are p rim arily a result of chrom ium depletionad jacent to the carbide, but dep end also on

carbide m orpho logy and the tim e availab leto heal chrom ium dep letion during cooling

through the carbide precipitation tem peraturerange.

Titanium and Niobium(Columbium) Carbonitrides.These carbonitrides occur prim arily in thestabilized ferritic grades, but m ay also occur

to a sm all extent in the austenitic gradesbecause titanium m ay b e includ ed in the

deo xidation p rocedures. They have neg ligible

effects o n the properties o f the austeniticgrades. W hen titanium or niobium is used tostab ilize carbon and nitrogen in the ferritic

grades, the resulting carbonitride form s initiallyas nitride over the solidification tem perature

range. The nitride then takes on carbon as

the tem perature drop s through ab out 10 50 °C(19 20 °F). C onsequently, these p hases do no t

play a m ajor role in the corrosion behaviour ofproperly annealed ferritic grades. H ow ever, if

the annealing tem perature is too high, carbonand nitrogen can b e re-solutionized and

produce sensitization by the precipitation ofchrom ium carbide during cooling through the

low er tem perature sensitization range. A lso,the titanium and niobium carbonitrides are

attacked b y som e strong acids and can actas initiation sites for brittle fracture in the

ferritic grades.

Chromium Nitrides.The use of high nitrogen in the d up lex andaustenitic high-perform ance stainless steels

favo urs the occurrence of various chrom iumnitrides of w hich C r 2N is the m ost com m on.

N itrogen is q uite soluble in these highchrom ium grades at hot w orking and

annealing tem peratures; so these nitrides

generally form up on cooling below thesetem perature ranges. In the austen itic g rad es,

they can precipitate in the sensitizationtem perature range and usually appear as fine

intergranular precipitates that are difficult todistinguish from carbide and sigm a phase.

In the dup lex grad es, the m orpho log y ofchrom ium nitride precipitates is highly

dep endent on prior therm al history. W ithproper solution annealing and rap id co oling,

the typ ical forty to sixty percent austenitephase balance is ad eq uate to solutionize all

of the available nitrogen; so chrom ium nitride

is not norm ally a m icrostructural constituent.H ow ever, high annealing or ho t w orking

tem peratures and w elding w ill red uce theam ount of austenite available to solutionize

nitrogen . In this case even rap id co oling canresult in fine spherical and needle-shap ed

nitride precipitate w ithin the ferrite phase and

on ferrite-ferrite and ferrite-austenite grainboundaries. A s w ith chrom ium carbide, eitherslow co oling or heating w ithin an interm ed iate

tem perature range of about 650-950°C(1200-1740°F) w ill produce intergranular

nitrides that can be deleterious to corrosion

resistance.

Sigma Phase.S igm a phase can form in virtually all of the

high-perform ance stainless steels and it isprobab ly the m ost im portant second ary

phase in term s of its effects on corrosion andm echanical properties. Its high rate o f

form ation and potentially large volum efraction is favo ured by high chrom ium and

m olybdenum content. B ecause highchrom ium and m olybdenum are an essential

feature, m inim izing the occurrence of sigm a

phase can be a significant factor in the

Chromium Carbides.C hrom ium carbides arenever a significant

structural feature interm s of volum e

fraction because allthese stainless steels

are m elted w ith low

carbon content.N orm al annealing

tem peratures aread equate to solutionize

carbon in the stabilizedferritic grades and in

the dup lex andaustenitic grades

w here the austenitehas high so lubility for

carbon at annealingtem peratures. The

occurrence of carbides

is usually confined tofine intergranular



successful production and fab rication of the

m ore highly alloyed stainless steels. Theupper tem perature lim it of sigm a phase

stability is about 1050°C (1920°F). A ll thesegrades w ere d evelop ed to be free of sigm a

phase in the solution annealed condition.H ow ever, traces of sigm a are not uncom m on

in solution annealed austenitic grades

because of segreg ation in the starting castslab or ingot. The rapid precipitation kinetics

and high sigm a solvus tem perature in thesehighly segregated reg ions m ake it alm ost

im possible to produce m ill product totally freeof sigm a. O ne of the goals in annealing the

austenitic grades is to reduce so lidificationsegregation , and thus m inim ize sigm a phase.

The d uplex and ferritic g rad es are less proneto so lidification segregation, and so any

sigm a p hase that occurs is usually the resultof precipitation below the sigm a solvus

tem perature. P recipitation usually occurs on

ferrite-ferrite and ferrite-austenite g rainboundaries. The form ation of sigm a phase

results in chrom ium and m olybd enumdepletion in the surrounding m atrix, and this

is believed to be the cause of red ucedcorrosion resistance usually associated w ith

its presence. This effect is m ost pronounced

w ith sigm a prod uced at low tem perature andsho rt tim es. H om ogenization and w orkingtreatm ents can m inim ize the effect so that

sm all am ounts form ed during solidification w illhave little effect in w rought products. S igm a

also adversely affects ductility and toughness

because it is a hard and brittle p hase. Theseeffects are very p ronounced in the ferritic and

duplex grad es and are significant in theaustenitic g rades as w ell.

Chi Phase.C hi phase form s over about the sam etem perature range and has ab out the sam e

kinetics of form ation as sigm a p hase. Itoccurs in the ferritic and duplex grades often

concurrent w ith sigm a, but usually in a m uchsm aller volum e fraction. If w ell developed, it

can be disting uished optically from sigm a by

its m ore b locky m orpho log y and higher

reflectivity. C hi also reduces corrosion

resistance and toug hness, but these effectshave been difficult to quantify because it

alw ays occurs as a m inor phase w ith sigm a.

Alpha Prime.A lpha prim e is a chrom ium -rich phase that is

resp onsible for the w ell know n 475°C (885°F)

em brittlem ent that occurs in the ferritic andduplex grades. It precipitates as very fine,

subm icrosco pic particles that are coherentw ithin the ferrite m atrix. W hile it cannot be

detected by optical m icroscope, its p resenceis usually accom panied by increased

hardness, a loss of co rrosion resistance, andred uced toug hness. It occurs over the 350-

550°C (660°F-1020°F) tem perature range. Itskinetics of form ation are co nsiderably slow er

than tho se of the higher tem peratureprecipitates (sigm a and chi), so it is unlikely

to form up on co oling from norm al w elding or

annealing operations. H ow ever, the ferriticand dup lex stainless steels can b ecom e

severely alpha prim e em brittled duringservice; so the upper service tem perature is

usually lim ited to less than about 300°C(570°F) for these g rad es.

KINETICS OF PHASEPRECIPITATION REACTIONS

The tw o principal elem ents that im provecorrosion resistance, chrom ium and

m olybdenum , also participate in the form ation

of m any of the dam aging interm etallic phasesthat m ay occur in the high-perform ance

stainless steels. The rate of form ation of thesephases can be very rap id. C onsequently, the

therm al treatm ents req uired for processing andfabrication, as w ell as service therm al cycles,

m ust take reaction kinetics into acco unt toensure that anticipated co rrosion and

m echanical properties are obtained. M ost ofthese grades have been develop ed on the

basis of estab lishing a com prom ise betw eenm axim izing corrosion resistance and retarding

precipitation reactions su fficiently to allow for

successful processing . R ed ucing carbon

content and adding

nitrogen retards m anyof these precipitation

reactions.

M ost stud ies o fprecipitation kinetics are

based on isotherm al heattreatm ents and

m etallograp hic and X-raydeterm inations of early

stages of phaseprecipitation. Iso therm al

techniques yield rapidkinetics in transform ation

diagram s. O n the otherhand, continuous co oling

therm al cycles, as usually

encountered



com m ercially, generally w ill retard kinetics.W hile m icrostructure is im portant, property

alterations d ue to precipitation w ill depend onthe stage of developm ent of the precipitate and

on the property in question. There are casesw here som e degree of precipitation can be

tolerated and still give useful properties. Thereare o ther situations w here p roperties can be

affected before precipitates are detected in them icrostructure.

AUSTENITIC STAINLESSSTEELS

The secondary phase transform ation kinetics of

a conventional austenitic stainless steel suchas Type 316 is characterized by very sluggish

ch i and sigm a transform ation (transform ation

takes hundred s of ho urs) and carbide kineticsw hich are highly dependent on the carboncontent. In the low carbon grad es, the tim e to

initiate carbide precipitation is about thirtym inutes to an hour, m ore than adeq uate to

carry ou t norm al annealing and w elding

operations w ithout causing sensitization. In thehigh-perform ance austenitic stainless steels,

the high chrom ium and m olybdenum contentsaccelerate chi and sigm a reactions; this effect

is only partially m itigated by the retarding effectof higher nickel and nitrogen . The higher nickel

and chrom ium contents also reduce carbo nso lubility; so these grades are intolerant of

carbon contam ination and have very rap idsensitization kinetics. They m ust be p roduced

w ith low carbon levels, and m any of thesegrades use a n itrogen addition to further retard

carbide precipitation. These grad es are a

com prom ise betw een efforts to obtain better

corrosion resistance and to sufficiently delaysecond ary phase reactions to allow successfulprocessing and fab rication. This has been

achieved, but in g eneral, co oling rates m ust befaster or section sizes m ust be sm aller than

they are for the low er alloyed conventionalaustenitic stainless steel grades.

A transform ation d iag ram for Type 316 stainless

steel is show n in Figure 7 to illustrate the

secondary phase initiation tim es in this relatively

low alloy grade. In Figures 8 and 9 , theaccelerating effect of 5% m olybdenum and the

retarding effect of 0.145% nitrogen areillustrated for a 17C r-13N i base com position

sim ilar to Type 316 . In the 5% m olybdenumbase com position, the start of both chi and

carbide precipitation is in the order of a fewsecond s w itho ut nitrogen; but the use o f

nitrogen alloying delays the start by an order ofm agnitude. In these grad es, the chi reaction

often leads or occurs at about the sam e tim eas the start of sigm a p recipitation, and at aboutthe sam e tim e as the start of carbide

precipitation.

Figure 7 Isothermal precipitation kineticsof intermediate phases inType 316 stainless steel annealed

at 1260°C (2300°F) 6

0.1 1 10 100 1,000 10,000


( ˚ C )

Time (minutes)

1100

1000

900

800

700

600

500

400

300

200

2012

1832

1652

1472

1292

1112

932

752

572

392

CarbideChi

SigmaLaves

Figure 8 Isothermal precipitation kineticsof intermediate phases in a 0.05C-17Cr-13Ni-5Mo alloy containing

0.039% nitrogen annealed at 1100°C (2012°F) 7

0.1 1 10 100 1,000 10,000


( ˚ C )

Time (minutes)

1100

1000900

800

700

600

500

400

300

200

2012

18321652

1472

1292

1112

932

752

572

392

Carbide

Chi

Sigma

Laves



In the high-perform ance austenitic stainlesssteels, the volum e fraction of interm etallic

phases, w hen they occur, is usually not verylarge. P recipitation usually occurs on austenite

grain boundaries w ith sim ilar m orphologicalfeatures reg ardless o f the specific p hase.

Therefore, the various phases are difficult todistinguish am ong them selves; and b ecause

they all have a sim ilar deleterious effect on

corrosion properties, it is often convenient to

m erely identify the start tim e for “all”precipitatesin studies aim ed at engineering applications.Th is has been d one for three com m ercial high-

perform ance grades com pared w ith Type 316in Figure 10 . The tem perature at the nose

of the precipitation start curve for the highperform ance grades 254 S M O , 904 L, and

317LM N is som ew hat higher than that ofType 316. This reflects the higher tem perature

stability of chi and sigm a in the high-

perform ance stainless steels com paredw ith the low er tem perature stability for carbide

in Type 316.

FERRITIC STAINLESS STEELS

The ferritic stainless steels are the least tolerantof secondary phases because of the intrinsic

low toughness of the ferrite structure and itslow solubility for the interstitial elem ents,

carbon and nitrogen. The com m ercial highperform ance ferritic g rades listed in Table 2 ar

m ade w ith w hat m ay be described as low(<600 pp m ) or very low (<250 ppm ) contents

of carbon plus nitrogen. H ow ever, stabilizationis still required and, in both cases, titanium

or niobium ad ditions are used to co ntrol thedetrim ental effects of these interstitial elem ents.

A n isotherm al transform ation d iagram for

Fe-26 C r alloys w ith 18 0 ppm (C +N ) is given

in Figure 11 . C hrom ium carbide and nitrideprecipitation can occur and lead to intergranular

attack if it occurs in the sensitizationtem perature rang e of about 500-800°C (930-

1470°F). This precipitation w ill occur in the verylow interstitial range as w ell as at higher levels.

In these stainless steels, titanium nitride has

very low so lubility in ferrite and exists as astab le p hase at all tem peratures below theso lidus. H ow ever, substantial so lubility exists for

the titanium carbide and the niobium nitride andcarbide ab ove about 11 00°C (201 0°F). A t low er

tem peratures, titanium , niobium , and chrom ium

carbide and nitride p recipitation can occur butw ill not generally produce sensitization if it

occurs above about 800°C (14 70°F). Thus,annealing treatm ents and successful w elding

are based on this stabilization effect.

Figure 9 Isothermal precipitation kineticsof intermediate phases in a 0.05C-17Cr-13N-5Mo alloy containing

0.145% nitrogen annealed at 1150°C (2102°F) 7

0.1 1 10 100 1,000 10,000


( ˚ C ) T e

m p er a t ur e ( ˚ F )

Time (minutes)

1100

1000

900

800700

600

500

400

300

200

2012

1832

1652

14721292

1112

932

752

572

392

Carbide

Chi Laves

Figure 10 Isothermal precipitation kineticsof several high-performance

stainless steels compared withType 316 stainless steel 8

0.1 1 10 100 1,000 10,000


( ˚ C )

Time (minutes)

1100

1000

900

800

700

600

500

400

300

200

2012

1832

1652

1472

1292

1112

932

752

572

392

Type 316904L

317 LMN

254SMO



S tabilization is believed to occur at these

tem peratures b ecause the d iffusion rate ofchrom ium in ferrite is high enough to rep len ish

chrom ium dep letion associated w ith theprecipitation. The kinetics for precipitation in the

stab ilization range have not been defined forthese stainless steels and so are show n b y

the dashed curve in Figure 11 . It is know n

that w ater quenching of thin sections cansubstantially suppress the p recipitation. This has

been used effectively w ith the high-perform anceferritic fam ily w here rap idly cooled thin sections

are used in heat exchanger applications.

P recipitation in the 500-800°C (930-1470°F)range w ill produce

sensitization andsubseq uent intergranular

corrosion in corrosiveenvironm ents for hold

tim es certainly m uch

sho rter than the m inim umone m inute used b y

D em o9. It is believed thatthe kinetics are sim ilar for

the higher interstitial,stabilized alloys, but w ill

dep end on the tim e spent

in the high tem peraturestabilization rangebefore co oling to the

sensitization range. Theslope of the sensitization

C -curve indicates that

som e chrom ium rep lenishm ent of the sensitizedgrain boundaries can occur during prolong ed

holds at sensitization tem peratures.

The nose of the sigm a precipitation curve liesat about 82 0°C (15 10 °F) and 30 m inutes for

a stabilized 25C r-4M o-4N i stainless steelas show n in Figure 11 . C hi and laves phase

precipitation follow s the sigm a phase kinetics atlow tem peratures, but their stability range

extends to higher tem peratures than doessigm a phase. K inetics are considerab ly slow er

than show n in Figure 11 w ith the lesser alloyed

26C r-1M o versions of these grad es. It occurs

after about tw enty-five m inutes in the 26C r-

3M o-3N i grade, and the m ost rap id tim e ofprecipitation can be just a few m inutes in the

29C r alloys.

Alpha p rim e p recipitation canno t be detected byoptical m etallograp hy but w ill produce substantial

changes in m echanical properties, especially

a reduction in toughness accom panied byhardening. The alpha p rim e initiation kinetics

show n in Figure 11 w ere determ ined based oninitial hardening in a 26C r-3M o-3N i stabilized

grade. In this w ork, som e hardening occurredafter one year at tem peratures as low as 315°C

(600°F), but no hardening w as observed after

three years at tem peratures of 300°C (572°F) and290°C (550°F). The alpha prim e transform ation

kinetics do not appear to vary m uch w ith alloycontent. This w as dem onstrated by N ichol et

al.12

, w ho found an initiation tim e o f ten hours forboth stab ilized 26C r-1M o and unstab ilized 29C r-

4M o-2N i alloys, the sam e tim e show n for the26C r-3M o-3N i grade in Figure 11 .

DUPLEX STAINLESS STEELS

The kinetics o f interm etallic phase precipitation

in the duplex stainless steels are influenced by

the often sim ultaneo us transform ation of delta

ferrite to austenite upon

co oling through thetem perature rang e of

about 1100-600 °C(2010-1110°F) and by

the strong effect ofnitrogen. The phase

equilibrium relationsh ips

discussed earlier im plythat these stainless

steels are nearly 100%ferrite at the solidus

tem perature andnearly 50% ferrite at

tem peratures belowabout 1000°C (1830°F).

Even up on cooling fromnorm al annealing

tem peratures o f abou t1050°C (1920°F), som e

reversion of ferrite to

austenite w ill take place.This austenite is often

term ed secondaryaustenite. Three

m echanism s of ferritereversion to austenite

Figure 11 Isothermal precipitation kinetics

of intermediate phases in ferritic stainless steels containing 26%chromium, 1-4% molybdenum,

and 0-4% nickel 9,10,11,12

0.1 1 10 100 1,000 10,000


( ˚ C )


Time (minutes)

1100

1000

900

800

700

600

500

400300

200

2012

1832

1652

1472

1292

1112

932

752572

392

Carbide and Nitride(Ti, Nb, Cr)

(no sensitization)

ChromiumCarbide and Nitride

( sensitization)

Sigma

AlphaPrime

TitaniumNitride Chi

Laves



and is stable at slightly low er tem peratures.S igm a phase usually occurs in greater

am ounts than ch i. B ecause it preced es the chireaction, and because the tw o phases have

sim ilar effects o n properties and are difficult todistinguish m etallograp hically, it is often

convenient to describe effects o f “sigm aphase”w hen dealing w ith the duplex stainless

steels. D uplex grad es that are m ore highlyalloyed in chrom ium , m olybd enum , and nickel

w ill have m ore rap id sigm a and ch i kinetics

than 2205, and the converse exists for thelow er alloyed grades. This is illustrated by the

dashed curves in Figure 12 sho w ing the startof sigm a and chi form ation in grad es 2304 and

2507, and o ccurs because chrom ium andm olybdenum and possibly m anganese

accelerate the precipitation kinetics. N ickel has

a sim ilar accelerating effect, but the effect m aybe a result of nickel prom oting austeniteform ation w ith resultant increased chrom ium

and m olybdenum partitioning to the ferritephase. H igh solution annealing tem peratures

and co ntinuous cooling tend to red uce the rate

of form ation of sigm a p hase.

A lpha p rim e hardening occurs q uite rapidlyin the ferrite phase, but not in austenite.

Therefore, the effect of alpha prim eprecipitation on the bulk properties of the

duplex stainless steels lags behind the initialform ation of alpha prim e in ferrite by a

substantial m argin. This is show n by the tw oalpha prim e initiation curves in Figure 12 , w ith

one based on hardness and the o ther ontoughness.

MECHANICALPROPERTIES

W hile the m ain driving force for the

developm ent of the high-perform ance stainlesssteels has b een corrosion resistance,

enhanced m echanical properties have alsobeen obtained in m any instances. This is

esp ecially true for the m etallurgically m orecom plex dup lex grades that have a good

com bination of strength and toug hnessw hen their structures are carefully controlled.

It pertains also to the nitrogen-enhancedausten itic grades, w hich have excellen t

toughness at strength levels w ell ab ove thestandard grades. This is significant from the

standpoint of cost, because thinner sectionsoften can help offset the higher costassociated w ith higher alloy content. This

benefit has been used to advantage in allproduct form s to red uce the cost of large

piping installations, large process units,pressure vessels, and pressure piping , and

to red uce the w eight of topside structureson offshore platform s.

B ecause tem perature and m etallurgical effects

on m echanical properties are q uite d ifferent foreach of the three grad e g roup s, they are

discussed separately in the follow ing sections.

Each section b eg ins w ith a description o f basicm echan ical properties for the solution annealed

co ndition as w ould be p rovided in m ill-produced product. P roperty changes related to

m etallurgical effects p roduced by fabrication,heat treatm ent, and service are then

considered .

AUSTENITIC STAINLESSSTEELS

The m echanical properties of the high-

perform ance austenitic g rad es p rovide an

excellent com bination of good strength,ductility, and toughness over a broad

tem perature range. Their go od im pact



“God and

the

Rainbow”

sculpture

from an

original idea

by Carl

Milles in

254 SMO ®

stainless

steel



strengths at low tem peratures are unique for

such high-strength m aterials. These grad es arestronger than the standard austenitic g rad es

because strength gradually increases as alloyco nten t increases. M ost of the alloying

elem ents used to im prove corrosion resistance

or co ntrol phase balance are also solutionstrengtheners as show n in Figure 13 . The m ost

potent strengthener in these steels is nitrogen,w hich is also beneficial to corrosion resistance

and for retarding the form ation of som einterm etallic phases. The effect of nitrogen on

strength is show n in Figure 14 , w here a near50% yield strength increase over Type 304

stainless steel is indicated for a nitrogencontent of 0.20% . This strengthening effect

dim inishes som ew hat at higher nitrogencontents, but com m ercial grad es are availab le

containing a no m inal 0.50% nitrogen w hich w ill

m eet m inim um yield strength specifications of420-460 M P a (61-67 ksi). W hile nitrogen and

other strengthening elem ents d im inish ductilitysom ew hat as show n in Figure 14 , these

grades still have su fficient ductility to handlem ost co ld form ing operations.

A list of the m inim um am bient tem perature

m echanical property req uirem ents for these

grades as defined by the A S TM S tand ardS pecification for plate, sheet and strip (A 240)is provided in Table 5 . A com parison of this

table to the grad e chem istries given in Table 1

sho w s that the specified m inim um strengthsalso increase w ith substitutional alloy content

and nitrogen content. This is illustrated in

Figure 15 , w here the m inim um specification

strengths of representative grad es w ithincreasing alloy content are com pared w ith

strength data for Type 316L. The A S M E C od eallow ab le design stress values given in Table 6also reflect these strengthening effects. Theallow ab le stress values for som e high-

perform ance grades are m ore than tw otim es that of Type 316L.

S trength increases at low tem peratures asshow n in Figure 16 , and this is accom panied

by little loss in ductility. The rate ofstrengthening at low tem peratures is not as

great as for Type 316 and m ost other standardgrades because the high perform ance grades

are very stab le w ith reg ard to m artensitetransform ation. This is an ad vantag e w ith

regard to ductility and toughness, and inap plications w here low m agnetic perm eability

is required.

These grades also have very good toughness

at room tem perature, even those that containsubstan tial nitrogen additions. This is illustrated

in Figure 17 , w ith fracture toughness andim pact data for a g roup of austenitic stainless

Figure 13 Solid solution strengtheningeffects by alloying in austenitic

stainless steels 17

0 2 4 6 8 10 12 14 16 18

C h a n g e i n Y i e l d S t r e s s ( M P a )

Ch an g ei nY i el d

S t r e s s ( k si )

Alloying Element (atomic %)

300

250

200

150

100

50

0

-50

44

36

29

22

15

7

0

-7

N

MnNi

Cu

Si V Mo

W

B

C

Co

Figure 14 Effect of nitrogen on the strength and ductility of Type 304 stainless steel 18

0 0.1 0.2 0.3 0.4

S t r e n g t h ( M P a )

Carbon (0.018-0.090%) plus Nitrogen (wt%)

116

101

87

73

58

44

29

15

0

800

700

600

500

400

300

200

100

0

Tensile Strength

Ductility

YieldStrength

Elongation80%

70%

60%

50%



UNS ASTM Tensile Strength Yield Strength Elongation HardnessName Number Specification (minimum) (minimum) (minimum) (maximum)

ksi MPa ksi MPa % Brinell HRB

Type 316L S31603 A 240 70 485 25 170 40 217 96Type 317L S31703 A 240 75 515 30 205 40 217 96 Alloy 20 N08020 A 240/B 463 80 551 35 241 30 217 96

Alloy 825 N08825 B 424 85 586 35 241 30 – –317LN S31753 A 240 80 550 35 240 40 217 96260 – – 80 550 40 275 35 217 –317LM S31725 A 240 75 515 30 205 40 217 96317LMN S31726 A 240 80 550 35 240 40 223 97204X – – 73 500 30 210 35 187 90310MoLN S31050 A 240 80 550 35 240 30 217 96700 N08700 B 599 80 550 35 240 30 – 90904L N08904 A 240/B 625 71 490 31 220 35 – –20Mo-4 N08024 B 463 80 551 35 241 30 217 9620 Mod N08320 B 620 75 517 28 193 35 – 95 Alloy 28 N08028 B 709 73 500 31 214 40 – –20Mo-6 N08026 B 463 80 551 35 251 30 217 9625-6MO1925 hMo

N08925/NO8926 A 240/B 625 94 650 43 295 35 – –

254N – – 94 650 43 300 35 217 96SB8 – – 79 550 37 250 35 – –254 SMO S31254 A 240 94 650 44 300 35 223 97 AL-6XN N08367 A 240/B 688 100 690 45 310 30 240 – YUS 170 – – 100 690 43 300 35 217 972419 MoN – – 120 820 67 460 30 – –4565S S34565 – 115 800 61 420 35 – –3127 hMo N08031 B 625 94 650 40 276 40 – –654 SMO S32654 A 240 109 740 62 425 35 250 –

Table 5 Minimum mechanical properties in basic ASTM specificationsfor high-performance austenitic stainless steels

Figure 16 Low temperature strengthof high-performance austenitic

stainless steels

˚F -418 -328 -238 -148 -58 32 122 212˚C -250 -200 -150 -100 -50 0 50 100


Temperature

1800

1600

1400

1200

1000

800

600

400

200

0

261

229

203

174

145

116

87

58

29

0

AL-6XN

AL-6XN

20 Cb-3

Type 316

20 Cb-3

Type 316

– – – – Yield Strength Tensile Strength

Figure 15 Strengthening effect of nitrogen in high-performance austenitic stainless steels as manifested in ASTM A 240 minimum strength requirements

T316L0.07% N

T317LMN0.15% N

25-6MO0.20% N

654 SMO0.50% N

M i n i m u m

S p e c i f i c a t i o n

S t r e n g t h

( M P a )

Mi ni m

um S p e ci f i c a t i on

S t r en g t h ( k si )

965

827

689

552

414

276

138

0

140

120

100

80

60

40

20

0

Yield Strength Tensile Strength



steels containing nitrogen ranging to over one

percent. Toughness falls off gradually at low ertem peratures but is still substantial even at

-20 0°C (-32 8°F) as show n in Figure 18 .

The high-perform ance austenitic grad es alsoretain their strength advantage o ver the

standard grad es at elevated tem peratures.Typical short-term elevated tem perature

strength d ata co m pared w ith Type 31 6L aregiven in Figure 19 . These grad es can p rovide

useful service to co nsiderably higher

tem peratures than the ferritic and duplexgrades because they are no t sub ject to alpha

prim e em brittlem ent. This is esp ecially true forsom e of the low er chrom ium -m olybdenum , or

higher nickel-alloyed grades such as 20C b-3.H igh tem perature stress rupture data for this

grad e are g iven in Figure 20 .

Figure 17 Effect of nitrogen in solid-solid solution on the toughness of annealed austenitic stainless steels at room temperature 19

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 F r a c t u r e T o u g h n e s s , K J c ( M P

√ m

)I m

p a c t E n er g

y ,A v

( J o ul e sx2 )

Nitrogen Content (weight %)

800

700600

500

400

300

200

100

0

KJc Av

Figure 18 Low temperature CharpyV-notch impact propertiesof high-performance

austenitic stainless steels

˚F -418 -328 -238 -148 -58 32 122 212˚C -250 -200 -150 -100 -50 0 50 100

E n e r g y

( J o u l e s )

En er g

y (f tl b

s )

Temperature

350

300

250

200

150

100

50

0

258

221

184

147

110

74

37

0

AL-6XN

20 Cb-3

Type 316

Table 6 High-performance austenitic stainless steels ASME allowable design stress values (ksi)

UNS ASME 38°C 93°C 149°C 204°C 260°C 316°C 371°C 427Name Number Specification (100°F) (200°F) (300°F) (400°F) (500°F) (600°F) (700°F) (800

Type 316L S31603 SA-240 16.7 14.2 12.7 11.7 10.9 10.4 10.0 9.6Type 317L S31703 SA-240 20.0 17.0 15.2 14.0 13.1 12.5 12.0 11.5

Alloy 20 N08020 SB-463 22.9 20.6 19.7 18.9 18.2 17.7 17.4 16.8 Alloy 825 N08825 SB-424 23.3 21.4 20.3 19.4 18.5 17.8 17.3 17.0317LM S31725 SA-240 20.0 16.9 15.2 14.0 – – – –317LMN S31726 A 240 20.5 18.9 16.7 15.6 15.1 – – –310MoLN S31050 SA-240 22.9 19.9 18.1 16.8 15.9 15.1 – –700 N08700 SB-599 22.9 21.0 19.0 17.7 17.1 16.5 – –904L N08904 SB-625 20.3 16.7 15.1 13.8 12.7 11.9 11.4 –20Mo-4 N08024 SB-463 22.9 20.6 19.2 18.1 17.0 16.0 15.2 14.620 Mod N08320 SB-620 18.7 17.3 16.3 15.4 14.5 13.8 13.2 12.7

Alloy 28 N08028 SB-709 20.7 18.9 17.7 16.5 15.4 14.4 13.6 12.820Mo-6 N08026 SB-463 22.9 20.7 19.0 17.5 16.3 15.3 14.5 13.925-6MO N08925 SB-625 24.9 23.2 21.3 19.8 18.3 17.3 16.9 16.91925 hMo NO8925 SB-625 24.9 23.5 21.3 19.8 18.3 17.3 16.9 16.9254 SMO S31254 SA-240 23.9 23.5 21.4 19.8 18.6 17.9 17.4 –

AL-6XN N08367 SB-688 27.1 26.2 23.8 21.9 20.5 19.4 18.6 18.0654 SMO S32654 SA-240 31.1 31.1 30.3 28.5 27.3 26.6 26.3 25.93127 hMo N08031 B 625 23.5 22.0 19.7 18.3 17.2 16.4 15.7 15.2




The tensile properties o f the ferritic grades

are characterized as having quite high-yieldstrength w ith useful but lim ited ductility. The

high-yield strength is due to the strong so lutionstrengthening effect of m olybdenum and nickel

in ferrite, and to the strong strengthening effectof sm all grain size that is typ ical for the ferrite

structure. Tensile strengths are about the sam e

as those found in the standard austeniticgrades b ecause ferrite, w hile having an initial

high rate o f w ork hardening at low strains, doesno t w ork harden to the sam e extent as

austenite at high strains. The lim ited ductility istyp ical of the ferrite structure. A sum m ary of

m inim um m echanical properties as specified inA S TM A 240 is provided in Table 7 . M inim um

yield strengths are as high as 515 M P a (75 ksi),and typ ical tensile e longation for m ill annealed

sheet is about 25-30% . These tensileproperties translate into high A S M E B oiler and

P ressure Vessel design stress values as show n

for w elded tub e in Table 8 .

The ferritic grad es have the shortcom ing ofexhibiting a distinct ductile-brittle transition

tem perature. W hile m ost m ill products areproduced w ith a fairly low transition

tem perature, the transition can occur atam bient or even higher tem peratures if the

grain size is coarse, or if interm etallic phases o r

significant am ounts of interstitially dissolvedcarbon o r nitrogen exist in the m icrostructure.

This has presented a p roblem both in theproduction of these grad es and in their

co m m ercial use in heavy sections, especiallyw hen w elding is involved. This is illustrated in

Figures 21 and 22 for a heat treatm ent thatw ould sim ulate the w elding of ferritic stainless

steels o f various carbon and nitrogen contents.These stainless steels have very good

toug hness and transition tem peratures below-50°C (-60°F) as initially stabilize annealed at

815°C (1500°F). H ow ever, a sub sequent

1150°C (2100°F) anneal and w ater quenchtreatm ent produced a d rastic increase in

transition tem perature even at m oderately low

Figure 20 Stress rupture properties of 20Cb-3compared with Types 316 and 347

stainless steels at 10,000 hours(extrapolated values)

˚F 752 932 1112 1292 1472 1652˚C 400 500 600 700 800 900

R u p t u r e

S t r e n g t h

( M P a )

Temperature

700

600

500

400

300

200

100

0

101

87

73

58

44

29

15

0

Type 347

20Cb-3 StainlessType 316

Figure 19 High temperature strength of austenitic stainless steels

˚F 32 392 752 1112 1472˚C 0 200 400 600 800



Temperature

900

800

700

600

500

400

300

200

100

0

130

116

101

87

73

58

44

29

15

0

T316LT317LN20Cb-3

AL-6XN

T316LT317LN20Cb-3

AL-6XN

YieldStrength

TensileStrength



Figure 21 Effect of nitrogen on toughness for

quarter-size Charpy V-notch impact specimens of 17Cr-0.010-0.057N- 0.004C ferritic stainless steels heat treated at 815°C + 1150°C for one hour

and water quenched 20

˚F -148 -58 32 122 212 302˚C -100 -50 0 5 100 150

I m p a c t

E n e r g y

( J o u l e s ) I m p a c t E n er g

y ( f t .-l b s. )

Temperature

200

150

100

50

0

147

110

74

37

0

0.010% N

0.022% N

0.032% N

0.057% N

Figure 22 Effect of carbon on toughness for

quarter-size Charpy V-notch impact specimens of 17Cr-0.002-0.061C- 0.010N ferritic stainless steels heat treated at 815°C + 1150°C for one

hour and water quenched 20

˚F -148 -58 32 122 212 302˚C -100 -50 0 5 100 150

I m p a c t

E n e r g y

( J o u l e s )

Temperature

200

150

100

50

0

147

110

74

37

0

0.002% C

0.012% C

0.027% C

0.061% C

Name UNS Number Tensile Strength Yield Strength Elongation Hardness(minimum) (minimum) (minimum) (maximum)


Type 444 S44400 60 415 40 275 22 – 8326-1S S44626 68 470 45 310 20 217 96E-BRITE 26-1 S44627 65 450 40 275 22 187 90

MONIT S44635 90 620 75 515 20.0 269 28RcSEA-CURE S44660 85 585 65 450 18.0 241 100 AL 29-4C S44735 80 550 60 415 18.0 255 25Rc AL 29-4-2 S44800 80 550 60 415 20.0 223 20Rc

Table 7 Minimum mechanical properties in basic ASTM sheet and plate specifications for high-performance ferritic stainless steels

Name UNS Number 38°C (100°F) 93°C (200°F) 149°C (300°F) 204°C (400°F) 260°C (500°F) 316°C (60

Type 444 S44400 14.6 14.6 14.1 13.8 13.5 13.126-1S S44626 16.5 16.5 16.4 16.2 16.0 15.7E-BRITE 26-1 S44627 15.8 15.8 15.5 15.4 15.4 15.4MONIT S44635 21.9 21.2 19.9 19.1 18.7 –SEA-CURE S44660 20.6 20.6 20.6 20.3 20.2 20.1

AL 29-4C S44735 18.2 17.9 17.6 17.5 17.2 17.0 AL 29-4-2 S44800 19.4 19.1 18.8 18.6 18.4 18.1

Table 8 High-performance ferritic stainless steels ASME allowable design stress values (ksi)




Tensile and yield properties of the d uplex

grades are quite high. Their ductility is b etw eenthat of the ferritic and austenitic grades.

S trength increases and ductility decreasesas the level of alloying increases, especially

nitrogen content. The attractive strengthproperties o f the duplex grades are, in part,

due to the com bined effect of ferrite in raisingthe yield strength and that of austenite in

providing a high tensile strength from strainhardening. M inim um yield strengths for sheet

and plate are as high as 550 M P a (80 ksi) as

show n in Table 9 .

The e levated tem perature strength of theduplex g rad es is also quite good ( Figure 23 ).

A S M E C od e design stresses are given in Table

10. These d esign stresses are considerab ly

higher than those for either the austenitic orferritic grades. The A S M E C ode allow ab le

design stresses are based on the low est valuesof either the yield or tensile strength. This

adversely affects both the ferritic and austeniticgrad es and favours the dup lex grades. Fo r

m ost duplex grades, A S M E C od e allow able

stresses are lim ited to 315°C (600°F) because

of alpha prim e em brittlem ent; the G erm an TüVcode sets a som ew hat low er m axim umtem perature. W hile this form of em brittlem ent

m ust be co nsidered , it is not as detrim ental to

room tem perature toughness as in the ferriticgrades because the austenite, w hich m akes up

half the m icrostructure, is unaffected by alphaprim e precipitation. Therefore, in certain

circum stances, it m ay b e possible to considerbrief higher tem perature service, for exam ple,

thin w all heat exchanger tubes w here short-

tim e, higher tem perature transients occasionallyoccur. H ow ever, m any design codes p roh ibit

such a p ractice.

The d uplex stainless steels retain toughnessdo w n to tem peratures low enough for m ost

engineering applications, but not to theextrem ely low tem perature of cryogenic service,

for w hich alloys w ith a com pletely austeniticstructure are req uired . Low -tem perature C harpy

im pact data for rep resentative grades testedw ith the plane of fracture transverse to the

rolling direction are given in Figure 24 . W hile

these grades exhibit a definite transitiontem perature, they exhibit useful toughness at

tem peratures as low as ab out -100°C (-15 0°F).H ow ever, toughness is not isotropic and is

reduced by high ferrite content. C om m ercialgrad es typically have ab out 40-60% ferrite in

the as-produced solution annealed condition.

This ferrite co nten t rep resen ts a goodcom prom ise am ong m any m echanical andcorrosion properties. H igh ferrite content

carbon and nitrogen

levels. A coarse grainsize and precipitation of

carbon and nitrogen inthe higher carbon and

nitrogen ferritic stainlesssteels caused this loss o f

toug hness. The vacuum -

m elted , extra low carbonand low nitrogen grad es

such as A L 29-4-2 havesuperior d uctile-brittle

transition tem peraturescom pared w ith the A O D -

refined ferritics.

Ferritic stainless steelsalso have a service

tem perature lim itationrelated to the em brittling

effect of alpha p rim e

precipitation. For thisreason, the AS M E C ode

allow able stresses form ost of these grad es are

lim ited to 600°F (315°C )m axim um . A som ew hat

low er m axim um service

tem perature should beco nsidered forapplications invo lving

extrem ely long servicetim es.

Name UNS Number Tensile Strength Yield Strength Elongation Hardness(minimum) (minimum) (minimum) (maximum)


Type 329 S32900 90 620 70 485 15.0 269 283RE60 S31500 92 630 64 440 30.0 290 30.52304 S32304 87 600 58 400 25.0 290 3245M – 85 588 57 392 40.0 277 2944LN S31200 100 690 65 450 25.0 293 –2205 S31803 90 620 65 450 25.0 293 317-Mo PLUS S32950 100 690 70 485 15.0 293 32DP3 S31260 100 690 70 485 20.0 290 –UR 47N – 100 690 72 500 25.0 – –64 – 90 620 65 450 18.0 302 32255 S32550 110 760 80 550 15.0 302 32DP3W S39274 116 800 80 550 25.0 – 32100 S32760 108 750 80 550 25.0 270 –2507 S32750 116 795 80 550 15.0 310 32

Table 9 Minimum mechanical properties in basic ASTM sheet and plate specifications for high-performance duplex stainless steels



red uces the toug hness and the transitiontem perature, especially w hen ferrite is in excess

of abo ut 80% as show n in Figure 25 . H ighferrite contents are a possibility under certain

w elding co nditions. The duplex structure is alsodirectional in term s o f the distribution of ferrite

and austen ite in w rought products. This w illresult in low er toughness w hen the fracture

path is p arallel to lam ellar ferrite bands.

Fracture toughness d ata using J-R curvesillustrate this in Figure 26 , w here p late tested

at various o rientations relative to the rollingdirection exhibits increasing toughness as the

long specim en direction becom es parallel tothe rolling direction.

The fatigue properties of the duplex stainless

steels are also q uite good as a consequence of

their high-yield strengths.S om e rep resentative

data com paring D P 3 toType 316 stainless steel

are given in Figure 27 .

Figure 23 High temperature strength of duplex high-performance stainless steels

˚F 32 212 392 572 752 932 1112 1292 1472˚C 0 100 200 300 400 500 600 700 800



Temperature

900

800

700

600

500

400

300

200

100

0

130

116

102

87

73

58

44

29

15

0

7-Mo Plus

255

7-Mo Plus

255

Type 316L

Type 316L

– – – – Yield Strength Tensile Strength Figure 24 Charpy V-notch impact properties

of wrought high-performance duplex stainless steels

˚F -418 -328 -238 -148 -58 32 122 212 302˚C -250 -200 -150 -100 -50 0 50 100 150

E n e r g y

( J o u l e s )

Temperature

300

250

200

150

100

50

0

221

184

147

110

74

37

0

2205

3RE60

Type 316

2507

Table 10 High-performance duplex stainless steels ASME allowable design stress values (ksi)

UNS ASME 38°C 93°C 149°C 204°C 260°C 316°C 343

Name Number Specification (100°F) (200°F) (300°F) (400°F) (500°F) (600°F) (650°

Type 329 S32900 SA-240 25.7 25.7 24.8 24.3 24.3 – –3RE60 S31500 SA-789, SA-790 19.6 18.9 18.1 18.0 18.0 18.0 18.02304 S32304 SA-240 24.9 24.0 22.5 21.7 21.3 21.0 –44LN S31200 SA-240 28.6 28.6 27.1 26.3 26.1 26.1 –2205 S31803 SA-240 25.7 25.7 24.8 23.9 23.3 23.1 –7-Mo PLUS S32950 SA-240 28.6 28.5 27.0 26.4 26.4 26.4 –DP3 S31260 SA-240 28.6 28.5 27.1 26.4 26.3 26.3 26.3255 S32550 SA-240 31.4 31.3 29.5 28.6 28.2 – –DP3W S39274 SA-789, SA-790 33.1 33.1 31.6 31.4 31.4 31.4 –100 S32760 SA-240 33.1 31.0 29.4 29.0 29.0 29.0 –2507 S32750 SA-789, SA-790 33.1 33.0 31.2 30.1 29.6 29.4 –



PHYSICALPROPERTIES

A m bient tem perature physical properties

are given in Tables 11-13 for each high-perform ance stainless steel fam ily. S elected

elevated tem perature values are g iven in Table

14-16 . In each of these tables, data are

includ ed for one or m ore standard grades to

provide a b asis for com parison. These dataare prim arily from m anufacturers’data sheets,and there are cases w here sim ilar grad es

have identical properties. This suggests

that, in som e cases, ind ep endent propertydeterm inations for sim ilar grad es m ay no t have

been m ad e. A lso, in m any cases, differences inphysical property values am ong grad es are

very slight, and it is likely that som e of thesem erely reflect differences in test procedures.

It is useful to com pare the properties of each

fam ily of high-perform ance stainless steels w iththose of Type 316. First, the overall physical

properties are not greatly d ifferent from those

of the standard grades in each grad e class.S econd , for m any physical properties w here

data are lacking, values for the standardgrades m ay p rovide a useful approxim ation.

Figure 25 Effect of ferrite on the CharpyV-notch impact properties of awrought high-performanceduplex stainless steel 21

˚F -418 -328 -238 -148 -58 32 122 212 302˚C -250 -200 -150 -100 -50 0 50 100 150

E n e r g y

( J o u l e s )

E n er g y ( f t .-l b s. )

Temperature

300

250

200

150

100

50

0

221

184

147

110

74

37

0

40%

60%

70%

80%

Ferrite

Figure 26 J-R curves for duplex stainless steel specimens machined alongdifferent angles from the

longitudinal plane 22

J I n t e g r a l ( M J / m

. e 2 1 )

Delta a (mm)

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

Transverse

1545 60 75

Longitudinal

0 1 2 3 4

30

20%

Figure 27 Fatigue strength of a duplex stainless steel compared withType 316 austenitic stainless

steel at a frequency of 0.5 Hz

S t r e s sAm

pl i t u d

e ( k si )

Number of Cycles

S t r e s s A m p l i t u d e

( K g f / s q . m

m )

70

60

50

40

30

20

10

0

99

85

71

57

43

28

14

0

Austenitic Type 316

Duplex DP3

10,000 100,000 1,000,000 10,000,000 100,000,000

Tested in Air– – – Tested in 3%

Salt Solution



Table 12 Ambient temperature physical properties of high-performanceferritic stainless steels

Name UNS Number Density Specific Heat Electrical Resistivity Young’s Modulusg/cm3 lb/in3 J/kg°K Btu/lb/°F micro ohm-m micro ohm-in. GPa ksi x 1000

E-BRITE 26-1 S44627 7.66 0.280 427 0.102 0.55 330 200 29.0MONIT S44635 7.80 0.281 460 0.109 0.64 390 – –SEA-CURE S44660 7.70 0.278 500 0.120 0.66 400 214 31.0 AL 29-4C S44735 7.66 0.277 448 0.107 0.72 430 – – AL 29-4-2 S44800 7.70 0.280 448 0.107 0.72 430 200 29.0

Table 13 Ambient temperature physical properties of high-performanceduplex stainless steels

Name UNS Number Density Specific Heat Electrical Resistivity Young’s Modulusg/cm3 lb/in3 J/kg°K Btu/lb/°F micro ohm-m micro ohm-in. GPa ksi x 1000

Type 329 S32900 7.70 0.280 460 0.110 – – 200 29.03RE60 S31500 7.75 0.280 482 0.115 – – 200 29.02304 S32304 7.75 0.280 482 0.115 – – 200 29.02205 S31803 7.85 0.285 482 0.115 0.80 481 200 29.07-Mo Plus S32950 7.74 0.280 477 0.114 0.78 466 200 29.0DP3 S31260 7.80 0.281 502 0.120 – – 200 29.0UR 47N 7.85 0.285 480 0.114 0.80 481 205 29.7255 S32550 7.81 0.282 488 0.116 0.84 505 210 30.5100 S32760 7.84 0.281 – – 0.85 510 190 27.62507 S32750 7.79 0.280 485 0.115 – – 200 29.0

Table 11 Ambient temperature physical properties of high-performance austenitic stainless steels

Name UNS Electrical Magnetic Young’sNumber Density Specific Heat Resistivity Permeability Modulus

g/cm3 lb/in3 J/kg°K Btu/lb/°F micro ohm-m micro ohm-in. Oerst.(mu 200H) GPa ksi x 1000

Type 316L S31603 7.95 0.287 469 0.112 0.74 445 1.004 200 29.0Type 317L S31703 7.95 0.287 – – 0.79 475 – – – Alloy 20 N08020 8.08 0.292 502 0.120 1.08 651 1.002 193 28.0 Alloy 825 N08825 8.14 0.294 – – 1.12 678 1.005 – 28.320Mo-6 N08026 8.13 0.294 461 0.110 1.08 651 1.006 186 27.0317LMN S31726 8.02 0.290 502 0.112 0.85 512 – 200 29.0310MoLN S31050 – – – – – – – – –700 N08700 8.03 0.290 – – – – – – –904L N08904 7.95 0.287 461 0.110 0.95 572 <1.02 190 28.020Mo-4 N08024 8.11 0.293 456 0.109 1.06 635 – 186 27.020 Mod N08320 – – – – – – – – – Alloy 28 N08028 8.03 0.290 448 0.107 0.99 468 – 200 29.0SB8 N08932 – – – – – – – – –254 SMO S31254 7.95 0.287 498 0.119 – – 1.003 200 29.025-6MO N08925 /

8.15 0.294 461 0.110 0.88 528 <1.01 192 27.81925 hMo N08926 AL-6XN N08367 8.06 0.291 461 0.110 – – 1.003 195 28.2 YUS 170 – 7.98 0.288 – – 0.86 518 – 192 27.84565S S34565 8.00 0.290 510 0.122 0.92 554 – 190 28.03127 hMo N08031 8.03 0.290 440 0.105 1.00 602 – 195 28.3654 SMO S32654 8.00 0.290 510 0.122 0.78 470 – 188 27.6




Elastic Modulus in Tension GPa (ksi x 1,000) Type 316L S31603 200 (29.0) 194 (28.1) 185 (26.9) 177 (25.9) 169 (24.5) 160 (23.2)

Alloy 825 N08825 193 (28.0) 190 (27.6) 185 (26.8) 179 (25.9) 173 (25.1) 167 (24.2)317LMN S31726 200 (29.0) 194 (28.1) 186 (27.0) 179 (26.0) 171 (24.8) 163 (23.6)

Alloy 28 N08028 200 (29.0) 195 (28.5) 190 (27.5) 180 (26.0) 170 (24.5) 158 (23.0)1925 hMo N08926 193 (28.0) 186(27.0) 179 (26.0) 173 (25.1) 168 (24.4) 162 (23.6)4565S S34565 193 (28.0) 187 (27.1) 180 (26.1) 173 (25.1) 165 (24.0) 157 (22.9)

Mean Coefficient of Thermal Expansion - Temperature 20°C (68°F) to T - cm/cm/°C x 10 -6 (in./in./°F x 10 -6 ) Type 316L S31603 15.7 (8.72) 16.5 (9.16) 16.9 (9.38) 17.3 (9.61) 17.6 (9.78) 18.0 (10.0)

Alloy 20 N08020 14.7 (8.16) 14.9 (8.27) 15.2 (8.44) 15.5 (8.61) 15.9 (8.83) 16.1 (8.94) Alloy 825 N08825 13.1 (7.30) 14.2 (7.88) 14.9 (8.30) 15.3 (8.48) 15.6 (8.64) 15.8 (8.80)20Mo-6 N08026 14.7 (8.16) 14.8 (8.22) 14.9 (8.29) 15.3 (8.52) 15.7 (8.73) 16.0 (8.89)317LMN S31726 16.1 (8.94) 16.6 (9.22) 17.2 (9.55) 17.8 (9.89) 18.5 (10.3) –904L N08904 15.0 (8.33) 15.3 (8.50) 15.7 (8.72) 16.1 (8.94) 16.5 (9.17) 16.9 (9.39)20Mo-4 N08024 14.0 (7.78) 14.4 (8.00) 14.9 (8.29) 15.6 (8.66) 16.1(8.96) 16.5 (9.17)

Alloy 28 N08028 14.6 (8.11) 15.0 (8.00) 15.5 (8.50) 16.0 (9.00) 16.5 (9.50) 17.0 (9.44)254 SMO S31254 – 16.9 (9.40) – – – –25-6MO N08926 – 15.1 (8.40) – – – –1925 hMo N08926 14.4 (8.00) 15.0 (8.33) 15.7 (8.72) 16.1 (8.94) 16.4 (9.11) 16.7 (9.28)

AL-6XN N08367 – 15.3 (8.5) – – – 16.0 (8.9)4565S S34565 13.7 (7.61) 14.5 (8.00) 15.5 (8.60) 16.3 (9.00) 16.8 (9.30) 17.2 (9.50)3127 hMo N08031 14.0(7.78) 14.3 (7.94) 14.7 (8.17) 15.1 (8.39) 15.5 (8.61) 15.9 (8.33)

Thermal Conductivity - W/m °C (Btu in/hr ft2 °F) Type 316 S31603 14.0 (97) 14.9 (103) 16.0 (111) 17.3 (120) 18.6 (129) 19.9 (138)

Alloy 20 N08020 11.6 (81) 13.1 (91) 15.0 (104) 16.6 (115) 18.2 (126) 19.6 (136) Alloy 825 N08825 11.1 (77) 12.4 (86) 14.1 (96) 15.6 (108) 16.5 (115) 18.2 (126)20Mo-6 N08026 11.6 (81) 13.1 (91) 15.0 (104) 16.6 (115) 18.2 (126) 19.6(136)317LMN S31726 14.0 (97) – – – – –904L N08904 11.5 (80) 13.1 (91) 15.1 (105) – – –20Mo-4 N08024 11.5 (80) 13.1 (91) 14.9 (103) 16.7 (116) 18.3 (127) 19.7 (137)

Alloy 28 N08028 11.4 (79) 12.9 (89) 14.3 (99) 15.6 (108) 16.7 (116) 17.7 (123)254 SMO S31254 14.0 (97) – – – – –25-6MO N08926 16.7 (116) – – – – –

AL-6XN N08367 13.7 (95) – – – – –1925 hMo N08926 12.0 (83) 12.9 (89) 14.4 (100) 16.5 (114) 18.5 (128) 20.1 (139)4565S S34565 14.5 (101) 14.5 (101) – – – –3127 hMo N08031 12.0 (83) – – – – –

654 SMO S32654 8.6 (59) 9.8 (68) 11.3 (78) 12.6 (87) 14.5 (100) –

Table 14 Elevated temperature physical properties of high-performance austenitic stainless steels

Name UNS Number 20°C (68°F) 100°C (212°F) 200°C (392°F) 300°C (572°F) 400°C (754°F)

Mean Coefficient of Thermal Expansion - Temperature 20°C (68°F) to T - cm/cm/°C x 10 -6 (in./in./°F x 10 -6 ) E-BRITE 26-1 S44627 – 9.9 (5.5) – – –SEA-CURE S44660 – 9.7 (5.4) 10.2 (5.7) 10.5 (5.9) 10.8 (6.0) AL 29-4C S44735 – 9.4 (5.2) 9.7 (5.4) – 10.4 (5.8) AL 29-4-2 S44800 – 9.4 (5.2) – – –

Thermal Conductivity - W/m °C (Btu in/hr ft2 °F) E-BRITE 26-1 S44627 16.7 (116) 17.9 (124) 19.3 (134) 20.9 (145) –SEA-CURE S44660 16.4 (114) 18.3 (127) 20.5 (142) 22.5 (156) 24.2 (168) AL 29-4C S44735 15.2 (105) 16.4 (114) 18.0 (125) 19.6 (136) – AL 29-4-2 S44800 15.1 (105) 16.4 (114) 18.0 (125) 19.6 (136) –

Table 15 Elevated temperature physical properties of high-performanceferritic stainless steels



W ith regard to elastic constants, Young’sM odulus is highest for the ferritic grades and

slightly ab ove 200 G P a (29.0 x 10 3 ksi). The

low est values, about 185 M P a (27 .0 x 1 0 3 ksi),are for the high-nickel austenitic grades. Elasticm odulus d ata, determ ined for a g roup of these

austenitic g rades using four different testm ethods, are given in Figure 28 .

The ferritic grades have slightly low er densityand electrical resistivity, and higher m elting

points than Type 316 and the high-perform ance austen itic g rad es. The austen itic

grades w ith very high nickel have slightly higherdensity and electrical resistivity than Typ e 3 16.

The austen itic grad es w ith very high


Elastic Modulus in Tension GPa (ksi x 1,000) Type 329 S32900 200(29.0) 195(28.0) 185(27.0) – – –3RE60 S31500 200 (29.0) 190 (27.6) 180 (26.1) 170 (24.7) 160 (23.2) 150 (21.8)2304 S32304 200 (29.0) 190 (27.6) 180 (26.1) 170 (24.7) 160 (23.2) 150 (21.8)2205 S31803 200 (29.0) 190 (27.6) 180 (26.1) 170 (24.7) 160 (23.2) 150 (21.8)UR 47N – 205 (29.7) 194 (28.1) 181 (26.2) 170 (24.7) – –255 S32550 210 (30.5) 200 (29.9) 198 (28.7) 192 (27.8) 182 (26.4) 170 (24.7)2507 S32750 200 (29.0) 190 (27.6) 180 (26.1) 170 (24.7) 160 (23.2) 150 (21.8)

Mean Coefficient of Thermal Expansion - Temperature 20°C (68°F) to T - cm/cm/°C x 10 -6 (in./in./°F x 10 -6 ) Type 329 S32900 – 10.9(6.10) 11.0(6.30) 11.6(6.40) 12.1(6.70) 12.3(6.80)3RE60 S31500 12.6 (7.00) 13.0 (7.22) 13.5 (7.50) 14.0 (7.78) 14.5 (8.06) 15.0 (8.33)2304 S32304 12.6 (7.00) 13.0 (7.22) 13.5 (7.50) 14.0 (7.78) 14.5 (8.06) 15.0 (8.33)2205 S31803 12.6 (7.00) 13.0 (7.22) 13.5 (7.50) 14.0 (7.78) 14.5 (8.06) 15.0 (8.33)7- Mo Plus S32950 9.5 (5.27) 10.5 (5.83) 11.5 (6.39) 12.4 (6.89) 13.3 (7.39) 13.9 (7.72)UR 47N 12.0 (6.67) 12.5 (6.94) 13.0 (7.22) 13.5 (7.50) – –255 S32550 11.7 (6.5) 12.1 (6.72) 12.6 (7.00) 13.0 (7.22) 13.3 (7.39) 13.6 (7.56)2507 S32750 12.6 (7.00) 13.0 (7.22) 13.5 (7.50) 14.0 (7.78) 14.5 (8.06) 15.0 (8.33)

Thermal Conductivity - W/m °C (Btu in/hr ft 2 °F) Type 329 S32900 – – – – – –3RE60 S31500 16.0 (110) 17.0 (118) 19.0 (132) 20.0 (138) 21.0 (147) 22.0 (153)2304 S32304 16.0 (110) 17.0 (118) 19.0 (132) 20.0 (138) 21.0 (147 22.0 (153)2205 S31803 16.0 (110) 17.0 (118) 19.0 (132) 20.0 (138) 21.0 (147) 22.0 (153)

7- Mo Plus S32950 14.1 (97) 16.4 (114) 19.0 (132) 21.5 (149) – –UR 47N – 17.0 (118) 18.0 (124) 19.0 (132) 20.0(138) – –255 S32550 13.5 (94) 15.1 (105) 17.2 (119) 19.1 (133) 20.9 (145) 22.5 (156)2507 S32750 16.0 (110) 17.0 (118) 19.0 (132) 20.0 (138) 21.0 (147) 22.0 (153)

Table 16 Elevated temperature physical properties of high-performance duplex stainless steels

Swivel component in Böhler A903 for

offshore application



m olybdenum also have significantly low er

m elting tem peratures. The dup lex g rad es exhibitinterm ed iate values w ith respect to these

properties.

A t elevated tem perature, the m ain d ifferencesam ong these grad es are that the ferritic grades

have a significantly low er coefficient of therm al

expansion and higher therm al conductivitycom pared w ith any of the austenitic grad es.

This w ill offer advantages in som e heatexchanger applications. A m ong the austenitic

grad es, very high nickel low ers therm alco nductivity and expansivity. The duplex g rad es

exhibit interm ediate values for these properties,but are typ ically closer to those in ferritic

stainless steels and carbon steel. C oefficients oftherm al co nductivity and expansion for the three

stainless steel fam ilies are show n as a functionof tem perature in Figures 29 and 30 .

Figure 28 Young’s Modulus for a selection of standard and high-performance stainless steels using four different techniques 23

0 50 100 150 200 250GPa

304L

304316L

3162205 (1)

2205 (2)

2304

800H

282RE10

Figure 29 Thermal conductivity of high- performance stainless steel structure types comparedwith Type 316 stainless steel

˚F 32 212 392 572 752 932 1112˚C 0 100 200 300 400 500 600

T h e r m a l C o n

d u c t i v i t y ( W / m ˚ K )

T h er m

al C on d

u c t i vi t y ( B t u.i n / h r f t 2

˚ F )

Temperature

242322212019181716

15141312111098

13.9

12.7

11.6

10.4

9.2

8.1

6.9

5.8

5.2

4.6

High-Performance

Duplex

High-Performance

Austenitic

Type 316

High-Performance Ferritic

Figure 30 Mean coefficient of thermal expansivity for different high-performance

stainless steel structure typescompared with Type 316 stainless

steel (from 20°C to T)

˚F 32 212 392 572 752 932 1112˚C 0 100 200 300 400 500 600

C o e

f f i c i e n t o

f T h e r m a

l E x p a n s i o n

( c m / c m / ˚ C x

1 0

- 6 )

Temperature

20

15

10

5

11.1

8.3

5.6

2.8

High-Performance Duplex

High-PerformanceFerritic

Type 316




Pressurized

peroxide

(prepox)

reactor made

of 2205 duplex

stainless steel

installed in a

Swedish

pulp mill



CORROSIONRESISTANCE

The outstanding corrosion perform ance of thehigh-perform ance stainless steels is due not

only to their high absolute alloy content, butalso to the synergistic effects related to the

interaction o f high chrom ium and the otheralloying elem ents. For exam ple, even a sm all

am ount of nickel in a high chrom ium ferriticgrade w ill greatly extend its range of passivity

in reducing acids. M olybdenum becom es m oreeffective as an agent to resist chloride pitting

as chrom ium content increases. N evertheless,there are considerab le d ifferences am ong the

grad es in relation to the environm ent and the

m any po ssible form s of corrosion. A n exam ple

of this difference am ong three ferritic gradesw ith resp ect to pitting, crevice corrosion andstress corrosion cracking is g iven in Figure 31 .

P erhaps one o f the m ostform idable tasks facing the

co rrosion engineer usingthese grades is to identify

the optim um grade from aco rrosion standpoint.

RESISTANCE TOINORGANIC

ACIDS

Sulphuric Acid.The passivity-dependent

corrosion behaviour ofhigh perform ance

stainless steels insulphuric acid so lutions is

determ ined largely b y the oxidizing pow erof the specific sulphuric acid environm ent.

S ulphuric solutions can be quite variable inthis reg ard. M id-range acid co ncentrations

and high tem peratures prod uce w eakly

oxidizing conditions for pure solutions and,therefore, high general corrosion rates.

A eration and oxidizing ions such as ferric,cupric, nitrate, and chrom ates w ill increase

the oxidizing potential of dilute so lutions and

generally allow for stainless steels to m aintain

passive b ehaviour over broad er acidcom position ranges and higher

tem peratures. The presence of the chlorideor other halide ion can lead to pitting w hen a

stainless steel w ould otherw ise be expected

to disp lay stab le passive behaviour. Thepresence of the halide ion is an im portant

factor w hen considering perform ance insulphuric acid so lutions. The m ultiplicity o f

so lution factors and the p olarizationcharacteristics of any given grade w ill

produce a w ide range of possible corrosionrates. C orrosion rates can reach very high

values even in grades designed specificallyfor sulphuric acid service . Thus, w hile m any

of these stainless steels are very good insulphuric acid solutions, it is a lw ays prudent

to co nd uct in-plant co rrosion tests w hen

selecting m aterials for this service.

The first stainless steelsthat co uld be d efined as

high-perform ance stainlesssteels w ere tho se grad es

developed for sulphuricacid service. These are

som e o f the austen itic

grades d efined assubgroup A -I in thispublication. The grad es

in this subgroup are

characterized by highnickel co nten ts and

ad ditions of co pper as w ellas m olybd enum . A lloys

825 and 20C b-3 aregeneral purpose stainless

steels suitable for service across the entireacid com position range at tem peratures less

than ab out 60°C (140°F). The isocorrosionline for 20C b-3 in Figure 32 illustrates typical

behaviour for these g rades in p ure acid

so lutions. Their useful range is extended tosom ew hat higher tem peratures if oxidizing

ions are p resent as d iscussed above.H ow ever, because these grades contain

relatively low m olybdenum , the presence of

24 26 28 30 32 34 36Chromium wt. %

M o l y b d e n u m w t . %

7

6

54

3

2

1

0

Figure 31 Differences among three high- performance ferritic grades with respect to pitting, crevice, and stress corrosion 24

Fail by fracture or stress corrosion MgCI 2 solution

Fail by pitting and crevice corrosionin both tests

Resistant in FeCI3 at 50oC/120oFand in KMnO4-NaCI at 90oC/195oF

Resistant in permanganate-chloridetest at 90˚C/195˚F

26Cr-1Mo

29Cr-4Mo

27.5Cr-3.4Mo



chloride ions seriously reduces theirresistance, even in relatively d ilute solutions.

A lloy 20M o-6, co ntaining higherm olybdenum , w as develop ed to give better

resistance under pitting conditions and also

provides good resistance to general co rrosionin the m id-acid com position range.

Isoco rrosion curves for a num ber of other

high-perform ance stainless steels are alsoshow n in Figure 32 . These g rades can

provide good resistance at low acid

concentrations. They do no t perform as w ellas the sub group A -I grades in the m id- to

high-acid concentration range prim arilybecause o f their low er nickel contents. S om e

duplex and ferritic g rades are also show n in

Figure 32 to give good resistance at low

co ncentration in pure acid solutions.H ow ever, the data for these stainless steels

ap ply to the passive co nd ition; duplex andferritic grades, having low er nickel than

austenitic grad es, m ay easily becom e

depassivated (activated), resulting in veryhigh corrosion rates.

In dilute sulphuric acid so lutions containing

the chloride or other halide ions w here pittingis a possibility, the higher m olybdenum

austenitic g rad es in sub groups A -4 to A -6

can give better resistance than the g rades insubgroup A -1. This is illustrated in Figure 33w hich sho w s corrosion data for acid

solutions containing 200 and 2,000 ppmchloride ion. W hile the p resence of chloride

w ill reduce the resistance of all grades, the

effect is m uch less in those grades thatcon tain high m olybdenum . The good

perform ance of the grades in subgroups A -4to A -6 und er these cond itions m akes them

good cand idates for hand ling com bustionproduct acid cond ensates, w hich often

contain chloride, at m oderate tem peratures,w hile the grades in subgroup A -1 are m ore

likely to be successful in pickling andchem ical process ap plications w here the

chloride ion is less prevalent.

Sulphurous Acid.S ulphurous acid is a relatively w eak acid that

is norm ally encoun tered as condensate influe g ases containing sulphur dioxide. It w illcause pitting in Type 304, but can usually be

handled w ith Type 316 provided it is notaccom panied by sulphuric acid and chloride

or fluoride ions. H ow ever, m any flue gasescan b e very acidic and co ntain halide ions.

In these instances, the high-perform ancestainless steels w ill offer substantially better

corrosion resistance than Type 316.

Figure 32 Corrosion in non-aerated sulphuric acid - 0.1 mm/yr (4 mpy) isocorrosion curves

0 10 20 30 40 50 60 70 80 90 100


( ˚ C ) T em p er a t ur e ( ˚ F )

Sulphuric Acid Concentration (weight %)

160

140

120

100

80

60

40

20

0

320

284

248

212

176

140

104

68

32

Boiling Point Curve

MONITMONIT

2205 2507254

SMO

T316

654 SMO317LMN

904L

20 Cb-3

Figure 33 Corrosion in non-aerated sulphuric acid-chloride solutions - 0.1 mm/yr(4 mpy) isocorrosion curves

0 5 10 15 20 25 30 35 40 45 50


( ˚ C )


Sulphuric Acid Concentration (weight%)

140

120

100

80

60

40

20

0

284

248

212

176

140

104

68

32

Boiling Point Curve

AL-6XN200 ppm CI

904L200 ppm CI

654 SMO2,000 ppm CI

904L 2,000 ppm CI

904L 0 ppm CI



up to abou t 30 % acid. A t highertem peratures and acid co ncentrations, the

high-perform ance grad es w ill provide goodresistance up to boiling tem peratures

throug h acid concentrations up to about80% . C orrosion tests show great variab ility

w ith this acid, but typ ical behaviour isillustrated by generalized isocorrosion curves

in Figure 34 . G ood perform ance in the hightem perature/high acid co ncentration range is

obtained prim arily w ith grad es having high

chrom ium and nickel content and, to a lesserextent, high m olybd enum content. The

regions show n in Figure 34 for the variousausten itic grad e subgroups indicate this

general alloying effect. S om e of the duplexgrad es w ill also give good perform ance

in the m id-range acid concentrations,

presum ably due to their high chrom ium andm olybdenum con tents as w ell as the use oftungsten and copper in som e alloys.

W hen pho spho ric acid solutions contain the

fluoride or chloride ions, for exam ple, in

phosphoric acid production, stainlesssteels that contain high chrom ium and

m olybdenum give good perform ance. Thisis illustrated by tests in a w et-process

phospho ric acid solution show n in Figure 35

attack of sensitized grain boundaries, and it

is essential that low carbon grades free ofsensitization be used in hot so lutions.

In pure phospho ric acid solutions, Type 304w ill handle m ost acid co ncentrations from

am bient to m od erate tem peratures. Type316 w ill extend the range o f usefulness to

near the boiling point in so lutions containing

Phosphoric Acid.P ure p hospho ric acidso lutions are less

aggressive thansulphuric so lutions, but

are sim ilar in the sensethat they have relatively

low oxidizing pow er.

Therefore, stainlesssteel corrosion

rates can be highin the higher acid

co ncentrations at hightem perature. C orrosion

rates are very sensitiveto ions that affect

oxidizing potential orthat m ay initiate pitting.

A ccordingly, nitrateand ferric ions w ill

red uce co rrosion ratesand chloride and

fluoride ions w ill greatly

increase the corrosivityof pho spho ric acid

solutions. P hosphoricacid solutions can

produce intergranular

Figure 34 Corrosion in pure phosphoric acid solutions - 0.1 mm/yr (4 mpy) isocorrosion curves

0 10 20 30 40 50 60 70 80 90


( ˚ C )


Phosphoric Acid Concentration (weight%)

160

150

140

130

120

110

100

90

80

70

60

50

320

302

284

266

248

230

212

194

176

158

140

122

Group A-6

Group A-4Group A-3

Group A-2Group A-1

Boiling Point Curve

Type 316Type 304

High PerformanceAustenitic

Stainless Steels

Figure 35 Corrosion in 70% phosphoric acid contaminated with 4% sulphuric acid,60 ppm chloride, 0.5% fluoride,

and 0.6% ferric ion

˚F 140 158 176 194 212 230 248 266˚C 60 70 80 90 100 110 120 130

C o r r o s i o n

R a t e

( m m

/ y r ) C or r o si onR

a t e ( m p y )

Temperature

10.00

1.00

0.10

0.01

400

40

4

0.4

Alloy C

20Cb-3 Alloy 825

904L Alloy G

Alloy 28



The high chrom ium /high m olybdenum A lloy

28 and sim ilar grades such as 20 M o-6perform very w ell in environm ents o f this

kind in contrast to the low er chrom ium /m olybdenum grades in subg roup A -2.

Hydrochloric Acid.H ydrochloric acid is a very strong red ucing

acid. S olutions in all but the w eakestconcentration readily attack the standard

grad es at room tem perature. In ho t solutionscorrosion rates are very rapid w ith hydrogen

evolution; so the standard grades aregenerally not considered suitable for handling

this acid. P itting can also occur in w eakso lutions, especially if surfaces that have

co ntacted the acid are allow ed to dry. A ny

stainless steel that has been in contactw ith hydrochloric acid should alw ays be

thoroughly rinsed afterw ard.

The high-perform ance stainless steelsdem onstrate im proved resistance to general

acid attack b ecause their higher chrom iumand nickel co nten ts help m aintain a stable

passive film . They are also m ore resistantto chloride pitting because of their high

chrom ium and m olybdenum contents. The

general behaviour of these stainless steels inhydrochloric acid so lutions is depicted in

Figure 36 . Even these stainless steels,

how ever, cannot be used to handleconcentrated solutions. The m ost highly

alloyed austenitic grad es such as 654 S M Ocan g ive useful resistance in am bien t

tem perature solutions approaching 10% acid.These g rad es are candidates for hand ling

dilute acid cond ensates at low to m oderatetem peratures. C orrosion rates increase

rapidly at higher tem peratures so that, at theboiling point, concentrations no greater than

abou t 1% m igh t be co nsidered for thesegrad es. B ecause of their high chrom ium

contents, the dup lex grades can also

provide good resistance in up to ab out 4%hydrochloric acid, and their corrosion rates

are som ew hat less tem perature-sensitive thanthose of the austen itic grad es ( Figure 36 ).

The ferritic grades, w hich co ntain som enickel, also dem onstrate good resistance in

w arm solutions up to abou t 1% acid; butthese grad es are readily dep assivated , or m ay

not estab lish passivity in the acid so lution iftheir surfaces are iron contam inated. This

tendency to depassivate is also a possibility

w ith the d uplex grad es w hich are sensitive to

preferential phase dissolution.

Hydrofluoric Acid.A lthough this acid is classified as beingsom ew hat w eaker than hyd rochloric acid, it

rem ains very co rrosive to m any m aterials ofconstruction including m ost stainless steels.

D ue to the hazardous nature of hydrofluo ricacid, any use of the high-perform ance

stainless steels in handling hydrogen fluoride

and its solutions should only be consideredw ith extrem e cau tion, and only after thorough

evaluation and consideration of all possiblesafety p recautions. The standard stainless

steel grad es are not considered resistan t toany but very dilute hydrofluoric acid so lutions

even at roo m tem perature. For exam ple, a0.1% solution at 60°C (140°F) w ill produce a

corrosion rate exceeding 0.60 m m /yr (0.024in./yr) w ith Typ e 304. S om e of the high-

Figure 36 Corrosion in pure hydrochloric acid solutions - 0.1 mm/yr (4 mpy) isocorrosion curves

0.1 1.0 10.0 100.0

T e m p e r a t u r e ( ˚ C

)


Hydrochloric Acid Concentration (wt. %)

120

100

80

60

40

20

0

248

212

176

140

104

68

0

Boiling Point Curve

Type 304 Type 316 AL-6XN

654 SMO2507

904L

DP-3

3RE60



not usually offer im proved corrosion

resistance in so lutions of pure nitric acid.A lthough little inform ation is available, one

w ould expect that these grades m ight behavesim ilar to Type 3 16 because of their high

m olybdenum contents. They can, how ever,pass standard intergranular sensitization tests

as defined in A S TM S tandard P ractice A 26 2,

and can give good service in various m ixedacid solutions containing nitric acid w here the

perform ance of Type 30 4L m ay be lim ited.

There have been som e special gradesdeveloped sp ecifically for severe nitric acid

service such as Type 31 0L and A lloy 800 .S erviceability to higher tem peratures and high

acid concentrations is accom plished w ithhigh chrom ium , low m olybdenum , and low

im purity content. The higher chrom ium andlow er m olybdenum high-perform ance duplex

steel, 7-M o P LU S , provides a sim ilar

im provem ent and has seen extensive servicein severe nitric acid environm ents. The high

chrom ium ferritic stainless steels that do notuse titan ium stab ilization, such as A L 29-4-2,

also have good resistance to hightem perature nitric acid liquid and vapour

environm ents. D ata for these grad es in

Figure 38 illustrate their superiority overType 304 in nitric acids.

perform ance stainless steels can give useful

service at m oderate tem peratures and lowacid co ncentrations, especially w hen aeration

or oxidizing salts are present and in m ixedso lutions w ith sulphuric acid. In particular, the

subgroup A -1 grades such as 20C b-3 and825, w hich contain high nickel and copper,

can p rovide som e resistance und er theseco nditions. G rad es that contain high

chrom ium and m olybdenum along w ith high

nickel and copper provide g ood resistance indilute acid, especially if the chloride ion is

present. Exam ples such as 904L, 254 S M O ,A lloy 31 and 65 4 S M O are show n for dilute

pure acid so lutions in Figure 37 .

Nitric Acid.The standard austenitic stainless steel grad es

have very good resistance to nitric acidsolutions at all tem peratures up to the boiling

point except in solutions o f very high acidconcentration. This is show n for Type 3 04

stainless steel in Figure 38 . Therefore, Type304L and its stab ilized co unterparts are used

extensively in the p roduction and handling of

this acid. Type 316 has a higher co rrosionrate than Type 304 b ecause m olybdenum is

deleterious. G ood resistance in nitric acid isobtained by the use of chrom ium ; therefore,

the high-perform ance austenitic g rad es do

Figure 38 Corrosion of Type 304 stainless steel in pure nitric acid solutions compared with some high-performance stainless steels - isocorrosion curves in mm/yr

0 10 20 30 40 50 60 70 80 90 100


( ˚ C )

Nitric Acid Concentration (%)

220

200

180

160

140

120

100

80

60

40

20

0

428

392

356

320

284

248

212

176

140

104

68

32

1.27-5.4

1.27-5.4

>5.40.51-1.27

0.51-1.27

0.13-0.15

0.13-0.51

0.1AL29-4-2

0.7AL 29-4-2

Alloy 287-Mo Plus

0-0.13

0-0.13 0.1310L

Figure 37 Corrosion in pure hydrofluoric acid solutions - 0.1 mm/yr (4 mpy) isocorrosion curves

0 2 4 6 8 10


( ˚ C )


Hydrofluoric Acid Concentration (wt. %)

100

80

60

40

20

0

212

176

140

104

68

0

254 SMO

654 SMO

904L Alloy 31



that the duplex and ferritic grad es have even

greater corrosion resistance in form ic acidthan the austenitic grad es. H igh chrom ium

and m olybd enum contents are especiallyuseful in this environm ent.

Acetic Acid.A cetic acid is second only to form ic acid in

term s o f the corrosivity o f the organic acids.It can b ecom e highly red ucing at high

concentrations, and thus, very corrosive inhot so lutions, esp ecially if the chloride ion is

present. Typ e 3 04 w ill resist all concentrationsat m od erate tem peratures, and Type 31 6 w ill

norm ally resist acid production processco nditions to the atm ospheric boiling

tem perature. H ow ever, because o f their highm olybd enum contents, the h igh-perform ance

stainless steels can give superior service athigher tem peratures and w hen chloride and

other contam inants are p resent. A n exam ple

of this tem perature effect co m paring severalhigh-perform ance stainless steels to Type316 in an acetic acid-hydroxy acid solution is

given in Table 17 . The benefit of m olybdenum

in these alloys com pared w ith Type 304,w hich d oes not contain m olybd enum , is

esp ecially noticeable. W hen oxidizingcontam inants such as air and p eracids and

iron, copper and m anganese salts arepresent, stainless steels, w hich dep end on a

RESISTANCE TO ORGANIC ACIDS

FicTsol usatm reageT*l the r )TO ORGA/46 /l -in27620-20.00m



passive film , w ill show im proved

perform ance. U nd er severe p rocessco nditions, the high-perform ance stainless

steels w ould be exp ected to resist thesecontam inants. This contrasts w ith alloys like

M onel 40 0 that do no t develop a stab lepassive film in this environm ent and

consequently w ill suffer higher corrosion

rates. C hlorides present a m ajor hazard ofpitting and stress corrosion cracking w hen

processing acetic acid using the standardstainless steel grad es. The subgroup A -1

high-perform ance austenitic grad es provide am ajor benefit over Type 316 in regard to

stress corrosion cracking, and the grad esin subgroups A -3, A -4, and A -6 w ould be

expected to perform m uch better in term s ofboth p itting and stress corrosion cracking.

M any production p rocesses for acetic acid

involve an oxidation process that produces

other organ ic acids including form ic acid.These m ixed acids are also very corrosive at

high tem peratures. A ll three types of high-perform ance stainless steels –ferritic, duplex,

and austenitic –are m ore resistan t than Type316 as show n in Table 18 for three boiling

pure acids, and in Figure 40 for m ixed acetic

and form ic acids.

Higher C3 Through C8 Organic Acids.The low er chain length acids such as acrylicand propionic acid are very sim ilar to acetic

acid in their reactivity to m etals and can be

quite co rrosive at elevated tem peratures. Theperform ance of stainless steels in acetic acid

suggests that the high-perform ance stainlesssteels w ill give better service than Type 316

at high tem perature and can bridge the

perform ance gap betw een Type 316 and the

nickel-base alloys. For exam ple, A lloy 20 hasbeen show n to dem onstrate a n il co rrosion

rate com pared w ith 0 .08 m m /yr (3 m py) forTyp e 304 in the top extractor of a nitrile-typ e

acrylic acid process.

The higher chain length acids becom e less

corrosive w ith increasing chain length atany given tem perature. In m any cases the

standard grades are relatively unaffectedat low and m od erate tem peratures; but

dep ending on the tem perature, boiling point,and deg ree of disso ciation, a tem perature is

reached at w hich corrosion rates increaserap idly. In these circum stances the high-

perform ance stainless steels can beexp ected to give im proved service

com pared w ith Type 316.

Table 18 Corrosion rates in boiling organic acids, mm/yr (mpy) 26

Name UNS Number 45% Formic 88% Formic 10% Oxalic 20% Acetic 99% Acetic

Type 304 S30400 1.2 (48) 2.4 (96) 1.3 (50) 0.03 (1.0) 0.5 (18)Type 316 S31600 0.3 (11) 0.2 (9) 1.0 (40) <0.01 (0.1) 0.05 (2)E-BRITE 26-1 S44627 0.1 (3) <0.01 (0.1) 0.1 (3) 0.03 (1) 0.01 (0.4) AL 29-4-2 S44800 0.02 (0.7) <0.01 (0.1) 0.02 (0.7) <0.01 (0.1) <0.01 (0.1) Alloy 625 N06625 0.1 (5) 0.2 (9) 0.2 (6) 0.03 (1.1) 0.01 (0.4)

Figure 40 Corrosion of austenitic and duplex stainless steels in boiling mixturesof 50% acetic acid and varying

proportions of formic acid

0 5 10 15 20 25

C o r r o s i o n

R a t e

( m m / y r )

Formic Acid Concentration (wt. %)

0.30

0.25

0.20

0.15

0.10

0.05

0

12

10

8

6

4

2

0

Type 316LType 317L

Alloy 28

2205

254 SMO

2507No Attack



Fatty Acids.The industrial fatty acids are generally

innocuous to the standard stainless steelgrades at low and m od erate tem peratures.

H ow ever, at high tem peratures, co rrosivityincreases together w ith the possibility o f

pitting and crevice corrosion. This is the casew ith tall oil recovery and refining, w here Typ e

316 m ay becom e unsatisfactory w hen thereis an excess o f light ends and at high-end

process tem peratures. The g eneral effect ofincreasing tem perature on corrosion rates

provided in Table 19 show s that even Type

317 can provide substantially low er corrosionrates com pared w ith Type 316 . The m ore

highly alloyed stainless steel grades w illprovide further resistance to general attack

and better resistance to pitting and crevice

corrosion. This is illustrated in Table 20 forthree high-perform ance stainless steelscom pared w ith Typ e 316 in tall oil distillation

at 260°C (500°F).

RESISTANCE TO ALKALIES AND ALKALINE SALTS

C arbon steels, the standard stainless steelgrad es, and the high-perform ance stainless

steels w ill resist the strong alkalies such assod ium hydroxide (N aO H ) and caustic potash

(K O H ) at am bient and m od erate tem peratures.The w eaker alkalies and alkaline salts such as

sod ium carbonate (N a 2C O3) are not verycorrosive to these m aterials up to boiling

tem peratures. The oxidizing salts such assodium hyp ochlorite (N aO C l), ho w ever, can be

very corrosive to m ost m etals including thestainless steels. M any of the high-perform ance

stainless steels are superior to Types 304 and316 in strong alkalies at high tem perature, and

the ferritic g rades have b een used in severe

caustic evaporator ap plications. They also haveso m e utility in handling certain oxidizing salt

solutions such as liquor evaporators and bleacheq uipm ent using hyp ochlorites.

Sodium Hydroxide.The standard austenitic stainless steel grad esare often used to handle strong caustic

solutions at tem peratures higher than w herecarbon steels are lim ited by caustic cracking,

ab out 66°C (160°F), or by product ironcontam ination. Figure 41 show s that Types

30 4 and 31 6 can be used to slightly above

100°C (212°F) in up to about 50% sod iumhyd roxide w itho ut experiencing excessive

Table 19 Corrosion in refined tall oil, mm/yr (mpy) 25

Name UNSNumber 286°C (545°F) 300°C (572°F) 315°C (599°F) 330°C (626°F)

Type 302 S30200 4.57 (180) 12.7 (500) 20.3 (800) –Type 316 S31600 0.10 (4) 0.10 (4) 1.35 (53) 12.7 (500)Type 317 S31700 0.03 (1) 0.03 (1) 0.53 (21) –C-276 N10276 0.10 (4) 0.13 (5) 0.10 (4) –

Table 20 Tall oil distillation corrosion

Name UNS Molybdenum Corrosion RateNumber (wt.%) mm/yr (mpy

Type 316L S31603 2.65 0.89 (35.2)317LM S31725 4.32 0.29 (11.6)317LMN S31726 4.60 0.28 (11.2254 SMO S31254 6.09 0.20 (0.8)

Figure 41 Corrosion of Type 304 and Type 316 in sodium hydroxide solutions - isocorrosion curves in mm/yr 27

0 20 40 60 80


( ˚ C )

Sodium Hydroxide Concentration (wt. %)

300

250

200

150

100

50

0

572

482

392

302

212

122

32Melting Point

Boiling Point

Stress Cracking Zone

Apparent Stress-Corrosion

Cracking Boundary

<0.025

0.025

>0.75

>0.75

0.025-1.250.025-0.75



Alkalies Containing Oxidizing Impurities.W hen strong alkalies co ntain im purities,

esp ecially oxidizing salts, the high-perform ance stainless steels show good

perform ance. This is esp ecially true of theferritic grad es that have high chrom ium and

low nickel contents as show n in Table 21 forE-B R ITE 26-1 exp osed to sodium hydroxide

solutions containing N aC l and N aC lO 3

contam inan ts. C orrosion rates are som ew hat

higher than in pure solutions, but still are in avery useful range. These ferritic g rades have

co rrosion rates o r caustic cracking. H ow ever,corrosion rates increase rapidly as the b oiling

tem perature is reached . The austenitic andesp ecially the ferritic high-perform ance

stainless steel grades have significantlylow er general corrosion rates at the boiling

tem peratures o f strong sodium hyd roxidesolutions as show n in Figure 42 . A ll but the

subgroup A -2 g rades, w hich are no t m uchdifferen t in chrom ium and nickel than Typ e

316, have corrosion rates about 17.nFigur3 42



standard austenitic stainless steel and nickel-base alloys. Virtually all of the high-

perform ance grades exhibit no t only goodgeneral corrosion resistance in w hite liquors,

but also m uch im proved stress corrosioncracking resistance com pared w ith Types

304 and 31 6 as show n in Table 22 . Thissuperior stress corrosion cracking resistance

ap plies to m ost caustic environm ents.

CHLORIDE- AND OTHERHALIDE ION-CONTAINING

AQUEOUS ENVIRONMENTS

Pitting and Crevice Corrosion.O f the m any com m ercial and techn icalfactors resp onsible for the developm ent of

the high-perform ance stainless steels, none

has been m ore instrum ental than the needfor grad es w ith good resistance to pitting,crevice corrosion, and stress corrosion

cracking in aggressive chloride environm ents.Thus, the high-perform ance stainless steels

collectively offer better chloride resistance

than the standard stainless steel grades.This good perform ance is obtained by the

use of the alloying elem ents chrom ium ,m olybdenum , and nitrogen, all of w hich are

very effective in im proving resistance topitting and crevice co rrosion, and high nickel

and nitrogen co ntents for stress corrosioncracking .

The pitting and crevice corrosion of stainless

steels occurs by a local breakdow n ofthe passive film , and then the localized

developm ent of an anodic corrosion site

surrounded by a cathodic area that rem ains

passive. B y definition, crevice corrosionreq uires the presence of a dep osit, gasket,or som e other crevice-form ing object on the

surface to initiate corrosion. O therw ise,the tw o form s of corrosion are essentially

identical. Therefore, the various g rades o fstainless steel behave sim ilarly w ith regard

to these form s o f co rrosion except that,because crevices help initiate corrosion,

resistance to crevice corrosion is usually less

in the presence o f contam inants and

com pares very favo urab ly w ith the nickel 200and nickel-base alloys at som e o f the highest

tem peratures encoun tered in causticevap orator service .

P ap er pulp m ill w hite liquors a lso rep resen t

oxidan t-co ntam inated alkali environm ents inw hich the higher chrom ium levels of the

high perform ance stainless steels p roducereduced corrosion rates com pared w ith the

Figure 44 Corrosion of high performance stainless steels and other alloys in a simulated caustic evaporator liquid of (wt. %):

43NaOH + 7NaCl + 0.15NaClO 3 + 0.45Na 2SO 4

120 130 140 150 160 170 180 190 200

C o r r o s i o n

R a t e

( m m

/ y r ) C or r o

si onR

a t e ( m p y )

Temperature (˚C)

10.0

1.0

0.1

0.010

0.001

400

40

4.0

0.40

0.04

AL-6XN

Nickel 200

Alloy 625

E-BRITE 26-1

Table 22 Corrosion in white liquor at 127°C(261°F) in 154-day tests 29

Name UNS Number Corrosion Ratemm/yr mpy

E-BRITE 26-1 S44627 0.000 0.00 Alloy 600 N06600 0.005 0.20Type 329 S32900 0.008 0.30

Alloy 800 N08800 0.020 0.80 Alloy 400 N04400 0.023 0.90 Alloy 825 N08825 0.041 1.60Type 304 S30400 0.168 6.6 (SCC)*

Alloy 625 N06625 0.173 6.80Type 316 S31600 0.516 20.3 (SCC)*Carbon Steel – 0.886 34.90



than it is to pitting. B ecause m ost engineeredstructures w ill contain crevices, crevice

corrosion is m ore im portant from anengineering standpoint. The b alance o f this

discussion w ill em phasize crevice co rrosionw ith the understanding that general trends

w ill also apply to pitting.

A ll stainless steels behave sim ilarly w ithregard to variables that affect susceptibility to

crevice corrosion, and the high-perform ance

stainless steels are no exception. P recautionsand procedures that sho uld be follow ed

during fab rication and in the operation ofsystem s exposed to the threat of crevice

co rrosion are often m ore stringen t w ith thehigh-perform ance grades sim ply because the

environm ents usually are m ore aggressive.

M aintaining surface cleanliness, for exam ple,post-w eld rem oval of surface oxide, isan essential requirem ent for obtaining

satisfactory w eld perform ance in highchloride-containing acid or strongly oxidizing

environm ents. The general environm ental

effects w hich prom ote crevice corrosion

in stainless steels include high chlorideconcentrations, high acidity (low pH ), high

tem perature, high d issolved oxygen co ntent,and any environm ental constituent w hich

raises the corrosion p otential such asoxidizing m etallic ions and dissolved chlorine

gas. A ll these factors m ust be considered inrelation to w hether any grade of stainless

steel w ill be su itable for a given situation.

Ranking of Individual Grades.The evaluation of any grad e of stainless steel

for its “localized corrosion resistance”is a

difficult proposition because of the m anyvariables involved. For this reason it is best

to co nsider any evaluation as applying onlyto the specific test conditions em ployed.

N evertheless, it is helpful to have qualitative

ratings to m ake general com parisons and tom ake initial assessm ents o f suitability forservice. The ferric chloride test has b een

w idely used to develop the high-perform ancestainless steels; consequently, it is used

w idely to m ake relative com parisons am ong

them . This test isusually conducted

according to m ethodsdescribed b y AS TM

S tand ard Test M ethodG 48 or M TI-2, both

of w hich use anenvironm ent co nsisting

of 10% ferric chloride(FeC l3·6H 20) dissolved

in distilled w ater (6%FeCl3). It can provide

data based on the

pitting of a clean

Rings and discs made

of duplex and super duplex

grades for offshore application



surface or corrosion under artificial crevices.This test produces results that define a

“critical pitting tem perature”or a “criticalcrevice corrosion tem perature.”W hen

interpreting data from these tests, m anyim portant factors need to b e kept in m ind .

O ne of these is the inherent variability o f thetest, w hich has a standard deviation of ab out

2.5°C . Thus, w hen m aking co m parisonsam ong grad es, sm all differences in critical

tem peratures ( ≤5°) usually have no significant

m eaning. A nother im portant co nsiderationis that ferric chloride is highly o xidizing,

producing a corrosion potential w ith stainlesssteels of ab out 600 m v versus the standard

calom el electrode. This is far above w hatoccurs in m any natural environm ents such

as cooling w aters. Accordingly, the ferric

ch loride environm ent is very aggressive, andthe test does not yield results that translate

directly to natural environm ents.

The ferric chloride test is conducted byexposing sp ecim ens to p rogressively higher

tem peratures in 2 .5°C tem perature intervalsuntil pitting or crevice corrosion initiates over

a tim e interval w hich is usually an arbitrarilychosen tw en ty-four hours. The critical

pitting tem perature (C P T) or critical crevicetem perature (C C T) is defined as the m inim um

tem perature at w hich corrosion occurs.

Illustrative data for representative gradesevaluated in 10% ferric chloride are given in

Figure 45 . It show s that som e criticaltem peratures are m uch low er than the

tem peratures to w hich standard stainless

steels are often exposed in service, therebyillustrating the severity o f the test. For thisreason it cannot be used as a basis for

establishing service tem perature lim its. Thedata also illustrate that corrosion is m ore

likely to occur in the presence of crevices

because the C C T is alw ays low er thanthe C P T.

The high-perform ance stainless steels far

ou tperform the standard Types 30 4 and 31 6stainless steel grades in this test as the data

in Figure 45 show . The perform ance o f som eof these grades ap proaches that of the

corrosion resistant nickel-base alloys. Thereis a great range in p erform ance am ong the

differen t grades, due largely to chrom ium ,m olybdenum , and nitrogen alloying

differences. Various form ulae have been

developed to relate steel co m position to

critical corrosion tem peratures. The m ostcom m only used exp ression gives a p ittingresistance equivalen t (P R E) num ber, for

exam ple, PR E = % C r + 3.3% M o + 16% N ,w here the percentage o f these elem ents in

the steel is expressed in w eight percent.

S om e typical correlations of the P R E num berw ith several critical tem perature indices

(Figure 46 ) show the strong alloying effects of

Figure 45 Critical crevice and pittingcorrosion temperatures for

stainless steels and nickel alloys

6 5 4

S M O

2 3 0 4

2 2 0 5

2 5 5

2 5

0 7

A l l o y

G

A l l o y

6 2 5

C - 2

7 6

3 0 4

L

3 1 6 L

3 1 7

L

3 1 7

L M N

9 0 4

L

2 5 4

S M O


( ˚ C )


110

100

90

80

70

60

50

40

30

20

10

0

-10

230

212

194

176

158

140

122

104

86

68

50

32

14

CCT CPT



chrom ium , m olybdenum , and nitrogen on

pitting resistance. The fact that a differenttest m ethod w ill give a different critical

tem perature is also dem onstrated by theN aC l C P T curve being higher than the FeC l 3

C P T curve. A S TM S tandard Test M ethodG 150 evaluates the C P T in 1M N aC l using a

device co m m only called the Avesta C ell. This

electrochem ical test is a less severe m ethodof evaluation than the ferric chloride test

because the natural pH of sodium chlorideso lutions is near neutral, w hile that of the

highly oxidizing ferric chloride solution isabout 1.6.

A nother m ethod of evaluating and ranking

these alloys uses the 2% K M nO 4 - 2 % N aC ltest w hich sim ulates the highly oxidizing

cond itions of chlorinated m anganese-

co ntaining co oling w aters. S treicher 24 usedthis test to show that alloys w hich do not pit

at 90°C (194°F) w ould be resistant in severeheat exchanger ap plications.

N ew er m ethods b eing used to evaluate

resistance to localized corrosion are

beginning to provide quantitative predictionsof initiation based on solution chem istryw ithin crevices and the crevice gap w idth.

S om e representative w ork, show n in Table

23 and Figure 47 , show s that the 4.5%

and 6% m olybdenum high-perform ance

austenitic stainless steels can functionw ith m uch higher acidity and chloride ion

co ncentrations w ithin crevices beforeco rrosion initiates, as co m pared w ith low er

Figure 46 Critical pitting and crevice corrosiontemperatures for austenitic stainless

steel related to PRE numbers

10 20 30 40 50 60 70


( ˚ C )


PRE Number (Cr+3.3Mo+16N)

11010090

80706050403020100

-10-20

230212194

1761581401221048668503214-4

CPT in NaCI

CPT in FeCI3

CCT in FeCI3

Figure 47 Effect of crevice gap width on the initiation of crevice corrosion in ambient temperature seawater 33

0.01 0.10 1.00 10.0

C r e v i c e

C o r r o s i o n

R e s i s t a n c e *

*Dimensionless units based on the critical crevice solution

Average Crevice Gap Width (microns)

2,000

1,500

1,000

500

0

Crevice Corrosion

No Crevice Corrosion

Alloy 625

Alloy G Alloy 254 SMO

904LType 317

Type 316

Type 304

Table 23 Crevice corrosion initiation for various alloys related to their critical crevice solutions 33

Chloride ConcentrationName UNS Number pH Molar ppm Ratio to Seawater

430 S43000 2.9 1.0 35,000 1.84Type 304 S30400 2.1 2.5 88,750 4.68Type 316 S31600 1.65 4.0 142,000 7.48904L N08904 1.25 4.0 142,000 7.48 AL-6XN N08367 <1.0 6.0 213,000 11.22 Alloy 625 N06625 0.0 6.0 213,000 11.22



alloyed stainless steel grades. Likew ise,these grad es can w ithstand a m uch tighter

crevice gap. This consideration is esp eciallyim portant for system s that produce very

tight, severe crevices such as threadedconnections and com pression fittings.

NEAR NEUTRALENVIRONMENTS – NATURALWATERS AND BRINES

M uch of the availab le crevice co rrosion

inform ation on the high-perform ance stainless

steels com es from a considerab le b od y ofseaw ater crevice co rrosion exposure tests

cond ucted by m any investigators. These

expo sure data are based on coupon exposuresusing controlled crevices, w ith the resultscorrelated in som e w ay w ith g rad e com position

or a laboratory param eter such as the C C T.This testing has show n that in seaw ater at

am bient tem peratures crevice attack w ill notinitiate in grad es having a C C T (G 48) of ab out

35°C (94°F) or higher. Figure 48 illustrates C C Ttem perature versus crevice corrosion initiation

as d eterm ined in am bient seaw ater exposures.

The 35 °C (94 °F) C C T (G 48 ) tem peraturecriterion ap pears to hold, reg ardless o f w hether

the grade is austenitic, ferritic, or duplex. It alsoseem s to relate w ell to service experience

w here the sub group s A-4 and A -6 austeniticgrades, w hich have C C T (G 48 ) tem peratures

ab ove 35°C (94°F), are all co nsidered suitab lefor hand ling seaw ater at near am bient

tem peratures in ap plications such ascondenser tubing and piping. This suitability

appears to be lim ited to pitting resistance o n

clean surfaces and m oderate natural crevicesituations such as fouling. W ith very severe

crevices such as under gaskets, or at highertem peratures, m ore resistant m aterials m ay

be required. To illustrate this point, creviceco rrosion data for a large num ber of alloys

evaluated in filtered seaw ater are given in

Table 24 . In these tests, only so m e nickel-basealloys and high-purity ferritic stainless steelsw ere com pletely resistant.

B ased on service exp erience in brackish and

fresh w aters, chloride ion levels of about 1,000

and 5,000 pp m m axim um , for Types 316 and904L respectively, are reasonable lim its for

cooling w ater in conventional heat exchangerap plications. These lim its and the 35°C C P T

criterion can be used to develop a serviceabilityguide for other high-perform ance stainless

steels by relating anticipated w ater chloridelim its to the C C T. Figure 49 show s that a broad

range in resistance to natural w aters of varyingchloride content results from the relatively sm all

range of C C T (G 48) values existing am ong thevarious high-perform ance stainless steels.

B ecause of their low m olybd enum content, the

subgroup A -1 acid-resistant grad es are o nly

m arginally b etter than Type 316 in resistance tocrevice co rrosion. M ost of the other grad es,how ever, are far sup erior to Type 316 in their

capability to resist crevice corrosion in highchloride w aters.

There are ap plications involving heavy sections

w here som e localized co rrosion initiation m aybe acceptab le. In these circum stances it is

useful to have so m e estim ate o f the rate o f

Figure 48 Crevice sites attacked in seawater exposure at 35°C for a number of

standard and high-performance stainless steels having differentCCT temperatures 31

˚F 14 32 50 68 86 104 122 140 158˚C -10 0 10 20 30 40 50 60 70

S i t e s A t t a c k e d ( % )

Critical Crevice Temperature FeCI 3

1009080706050403020100

■ AusteniticFerritic

● Duplex



Table 24 Crevice corrosion ranking of alloys evaluated for 30 days in filtered seawater at 30°C 34

1

23

45

6789

1011121314

1516171819

2021222324

Hastelloy C-276Inconel 62529-429-4-229-4C(1)

MONIT

Crucible SC-1Ferralium 255

Hastelloy G-3Haynes 20 Mod

26-1S20Mo-6EB 26-1 (A.L.)

AL 4X

AL 6X254 SMOHastelloy G904L (Uddeholm)

AISI 216

254SFER254 SLXRex 734Type 317 LMNitronic 50

Jessop 700Type 316Carpenter 20 Cb-3Jessop 77744 LN

AISI 444 AISI 32934 LN

AISI 439

AISI 317L AISI 317L+Incoloy 825

15.522.329.629.528.825.3

25.626.2

22.821.6

25.023.925.920.2

20.420.022.220.520.0

29.419.921.319.521.1

20.717.519.420.825.0

18.927.016.8

17.7

18.918.322.0

54.761.0

0.12.20.84.1

2.15.6

43.725.5

0.233.4

0.124.4

24.617.946.824.7

6.0

22.225.0

9.414.513.7

25.210.733.225.6

5.9

0.14.2

13.8

0.3

12.215.844.0

15.58.54.04.03.83.8

2.93.2

7.05.0

1.05.61.04.4

6.46.15.84.72.5

2.14.72.74.12.3

4.42.42.24.51 .5

2 01.44.2

—

3.64.22.7

0.50.1

——

0.20.4

0.20.8

0.80.9

0.20.4

—1.4

1.40.51.51.58.0

1.71.63.81.34.8

1.61.60.41.41.8

0.40.31.6

0.3

1.71.50.4

0.1————

0.4

—1.8

1.8—

—3.3

—1.5

—0.81.81.6

—

0.11.7

—0.2

—

0.20.33.22.20.1

—0.1

—

—

—0.21.7

3.8 W3.6 Nb

——

0.6Ti—

0.5Ti0.19 N

3.5 Co0.5 Co

1.1 Ti—

0.1 Nb0.019 P

—0.2 N3.5 Co

—0.35 N

0.15 N0.04 N0.42N0.056 N0.26 N

0.28 Nb—

0.51 Nb0.24 Nb0.2 N

0.4 Nb—

0.14 N

0.4 Ti

0.056 N0.16 Co0.7 Ti

000000

12

12

4344

45456

56666

56666

666

6

666

0.000.000.000.000.000.00

0.050.08

0.210.46

0.300.530.460.50

0.620.510.870.740.64

0.900.921.001.071.10

2.001.933.102.903.35

1.211.291.04

0.72

1.921.092.42

0.000.000.000.000.000.00

0.050.16

0.210.92

1.21.61.82.0

2.52.63.53.73.8

4.55.56.06.46.6

1012161720

7.27.76.2

4.3

126.5

15

Rank Alloy Cr Ni Mo Mn Cu Other

Numberof sides (S)

attacked

Maximumdepth (D) ofattack (mm)

CC(S x D

Perforated

Attack Outside Crevice Areas

Composition (wt.%)



A nother app roach to grade selection w hen

som e localized co rrosion can be tolerated isbased up on m athem atical m od el predictions

for corrosion in w aters of various chlorideco ncentrations 32 . The g uidelines show n in

Figure 52 also incorporate the concept of

criticality o f service and the fact that the

pitting or crevice corrosion that m ight be

an ticipated. These propag ation rates are veryhard to p red ict because of geom etry and other

variab les. H ow ever, availab le d ata suggest thatthose g rades w ith a high C C T w ill have a

relatively low corrosion propagation rate even

if localized corrosion initiates. The initiation ofcrevice co rrosion versus C C T co rrelation in

Figure 48 also suggests the existence of such

a relationship. The existence of a relationship

is dem onstrated w hen crevice dep th dataare plotted versus the C C T as in Figure 50 .

O ther studies have show n sim ilar effects thatcorresp ond to the data of Figure 50 w hen the

crevice depth data are also rationalized interm s of tim e. Figure 51 provides d ata from

various so urces w ith test durations fromseveral m onths to several years. W hen

evaluated in term s of rate, m ost of the d atafall w ithin a band that provides an order of

m ag nitude estim ation of crevice co rrosion ratesas a function o f C C T (G 48). This also sho w s

that stainless steel grad es w ith a higher C C T

(G 48) w ill have low er rates o f crevice corrosionif corrosion does initiate.

Figure 49 Cooling water serviceability guidelines for stainless steel heat exchanger tubing based on alloyCCT temperature 31

˚F -22 -4 14 32 50 68 86 104 122 140˚C -30 -20 -10 0 10 20 30 40 50 60

W a t e r

C h l o r i d e

I o n C o n t e n t

( p p m )

Critical Crevice Temperature in 6% FeCI 3

100,000

10,000

1,000

100

Figure 50 Depth of crevice attack in seawater exposure at 35°C for stainless steels

having different critical crevicetemperatures 31

˚F 14 32 50 68 86 104 122 140 158˚C -10 0 10 20 30 40 50 60 70

M a x i m u m

D e p t h

( m m

)

Critical Crevice Temperature in 6% FeCI 3

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

-0.2

0.071

0.063

0.055

0.047

0.039

0.031

0.024

0.016

0.008

0

-0.008

Type 316

904L

254 SMO

■ AusteniticFerritic

● Duplex

Figure 51 Estimated crevice corrosion ratesfor stainless steels in near ambient temperature seawater

˚F 5 14 23 32 41 50 59 68 77 86 95 104 113 122˚C -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50

C r e v i c e

C o r r o s i o n

R a t e ( m m

/ y r )

Critical Crevice Temperature in ASTM G 48

1.00.90.80.70.60.50.40.30.20.1

0

0.0390.0350.031

0.0280.0240.0200.0160.0120.0080.0040

Type 316 2205 2507 254 SMO



Carpenter alloy

20Cb-3 ® (right)

displays very

high resistance

to hot sulphuric

acid compared

to Type 316

stainless steel

probability of failure is less than the probability

of attack. A n exam ple o f critical service w ouldbe thin w all tubing, w here the available d istance

for propagation w ould be sm all; no rm al servicew ould be heavier sections of m aterial for w hich

the propag ation rate w ill determ ine the tim e ofuseful service . W ith this approach, Type 316

can provide useful service under som ecircum stances at m oderate chloride levels, but

a high-perform ance stainless steel such as904L is necessary for critical service. H ow ever,

at high chloride levels such as seaw ater, a

grade m ore resistant than 904L is necessaryfor critical service, for exam ple, grades in

subgroups A -4, A -6, F-2, F-3, and D -3.

A s tem perature increases ab ove am bient,the aggressivity of m ost pitting and crevice

co rrosion environm ents increases for allstainless steels. This effect w ill be tem pered by

the declining solubility o f oxyg en in w ater athigher tem perature, by a peak in polarization



due to a peak in biological activity, or byoxyg en solubility product-tem perature relations

for other w ater constituents. A dditionally,co rrosivity in seaw ater passes through a

m axim um at approxim ately 40°C , thendecreases as b iofouling is red uced . For

applications involving cooling w ith cleanseaw ater w ith m etal tem peratures near

am bient, such as condensers, it is generallyaccepted that the sub group s A-4, D -4, F-2,

and F-3 high p erform ance stainless steels w ill

resist pitting and crevice attack w ith m oderatecrevices such as fouling , and they can b e used

in thin w all tube ap plications. These sam egrad e subgroups w ill becom e suscep tible to

localized corrosion in seaw ater at highertem peratures, as crevice severity increases, or

w ith increasing chlorination. For exam ple, these

grad es have b een found not suitab le for plateheat exchang ers hand ling fresh seaw aterbecause this type of heat exchanger often

operates at high tem perature and the gasketsrequired in their design create very severe

crevices. The subgroup A -6 high perform ance

austenitic stainless steels are candidatem aterials for these severe applications.

The effect of tem perature and chloride

concentration on crevice corrosion initiation forseveral austenitic stainless steels is show n in

Figure 53 . This figure is b ased on one-yearlaboratory tests in oxygenated synthetic sea

salt solutions that w ere acidified to pH 2.0 tosim ulate the corrosivity of natural seaw ater. A

strong tem perature effect is clearly indicated,but the superiority of high perform ance

stainless steels is also evident. M any of these

grad es can extend useful service tem peratures

to levels w ell above that of Type 316 in avariety of co oling w aters and other aq ueousenvironm ents. The very highly alloyed subgroup

A -6 austenitic stainless steels are useful w ellabove am bient tem perature in seaw ater and

brines, even w hen gaskets or other severecrevices are em ployed. This is illustrated in

Table 25 w hich gives d ata for several brinesand stainless steel grades ranging from

Type 316 to 654 S M O . 654 S M O stainless

Figure 52 Guidelines for selection of stainless steelsfor water service based on mathematical

modelling of corrosion rates andcriticality of service 39,40

100 1,000 10,000 100,000

C r e v i c e

C o r r o s i o n

R e s i s t a n c e *

*Dimensionless units based on the critical crevice solution

Chloride Ion (ppm)

2,500

2,000

1,500

1,000

500

0

Minimum Service >1 in 10

Critical Service <1 in 10,000

Normal Service <1 in 10

Ratios relate to probability of crevice initiation in severe crevices

904L

Type 316Type 304

Figure 53 Effect of temperature and chloride onthe initiation of crevice corrosion on

austenitic alloys in aerated synthetic

sea salt solutions at pH 2 41

100 1,000 10,000 100,000


( ˚ C )

Chloride Ion (ppm)

100

90

80

70

60

50

40

30

20

100

212

194

176

158

140

122

104

86

68

5032


No Crevice Corrosion

Crevice Corrosion904L

Alloy 625

254 SMO317 LMN

Type 316



steel is the only g rade w hich exhibits no pittingor crevice attack to the m axim um test

tem perature o f 90°C , regardless of w hether the

brines are aerated or not. The effect of oxygenis also show n in Table 25 ; corrosion

perform ance is im proved w hen the brines havebeen d eaerated w ith nitrogen. For a d etailed

discussion on the selection of stainless steelsfor service in these environm ents, see the

N iD I publication N o. 11 003, “G uidelines forS election of N ickel S tainless S teels for M arine

Environm ents, N atural W aters and B rines”.

INFLUENCE OFMICROBIAL ACTIVITY

There are circum stances w here m icrobialactivity can influence the corrosion process.

This usually involves m icrobes w hich

m etabolize sulphur com pounds, prod ucing anaggressive acidic hydrogen sulphide-co ntaininglocalized environm ent. Less frequently it

invo lves a com bination of m icrobes and aunique chlorine-containing environm ent w hich

oxidizes certain cations, including iron andm ang anese, prod ucing a localized environm ent

having a highly oxidizing corrosion potentialrelative to stainless steels. In so m e situations

w here this m icrobial activity is present, the

standard stainless steel grades w ill undergolocalized co rrosion that w ould not have

occurred otherw ise. This is know n asm icrobiologically influenced corrosion (M IC ).

M IC is m ost likely to occur in environm entshaving high m icrobial population of the req uired

species and relatively stag nant co nditions atnear am bien t tem peratures. M etallurgically,

w elds are m ost suscep tible, especially poorly

cleaned w eld and heat-affected zone surfaces.This form of corrosion is know n to occur inTypes 304 and 316 stainless steels.

It is natural to exp ect that those stainlesssteels that have greater intrinsic resistance to

localized corrosion w ill have greater resistanceto M IC , and this is indeed the case. A review of

rep orted incidences of M IC in stainless steelshas identified no service failure of any high-

perform ance stainless steel grad e w herem icrobial activity w as conclusively

dem onstrated to have been present 43 . W hileit is d ifficult to produce this corrosion in the

laboratory, this review also show ed thatlaboratory studies centering m ostly on the

subgroup A -4 6% m olybdenum austenitic

stainless steel grad es have not producedany convincing data to sug gest that M IC

represents a threat to the serviceability o f

Table 25 Localized corrosion of stainless steels in 90°C (194°F) sodium chloride solutions 42

Effect of alloy, pH and aeration

20,000 Cl, pH 4, Aeration 100,000 Cl, pH 4, AerationName UNS Number C P W S E C P W S E

Type 316 S31600 – X X – 0 – X X – X2205 S31803 X 0 0 0 0 X 0 0 0 X904L N08904 X 0 0 – X X 0 X – X254 SMO S31254 X 0 0 – 0 X 0 0 – X654 SMO S32654 0 0 0 – 0 X 0 0 – 0

100,000 Cl, pH 8, AerationType 316 S31600 – X 0 – X2205 S31803 X 0 X 0 X904L N08904 X 0 X – X254 SMO S31254 X 0 0 – 0654 SMO S32654 0 0 0 – 0

100,000 Cl, pH 4, N2 Purge 100,000 Cl, pH 8, N2 PurgeType 316 S31600 – 0 X – 0 – X X – X2205 S31803 X 0 0 0 X X 0 X 0 0904L N08904 X 0 X – 0 X 0 X – 0254 SMO S31254 0 0 0 – 0 0 0 0 – 0654 SMO S32654 0 0 0 – 0 0 0 0 – 0



these stainless steels. O ne w ould exp ect that

resistance to M IC w ould im prove w ith grad esthat have a higher critical pitting or crevice

tem perature; so interest in dealing w ith thisprob lem has em phasized the subgroup A -4

austenitic stainless steels. They have been usedextensively in nuclear pow er plan t service w ater

and em ergency cooling system s w here

stagnant conditions have produced M IC -relatedfailure in coated carbon steel or

Type 304 and Type 316 piping.

OXIDIZING HALIDEENVIRONMENTS –CHLORINATED COOLINGWATERS AND BLEACHSOLUTIONS

The aggressivity of environm ents containinghalides, in term s of localized corrosion,

depends on the halide, pH , tem perature, and

the oxidizing pow er of the oxidant. B rom ideis the m ost aggressive halide in near neutral

so lutions, follow ed by chloride; iodide andfluoride are relatively innocuous. In acid

so lutions, fluoride can b e very aggressive.S trong oxidizers can act to raise the stainless

steel corrosion potential above its p itting or

crevice corrosion potential for any givenhalide. H igh tem perature and low pH w ill alsocontribute tow ard producing very co rrosive

co nd itions. Exam ples of situations w heresuch environm ents are encountered includ e

chlorination for fouling control in seaw ater-

co oled heat exchangers, and especially in thepulp bleaching step in p ap er production

w here a variety of strong oxidan ts are used.

The effect of chlorination on the corrosionpotential is illustrated in Figure 54 for the case

of 254 S M O exposed in natural seaw ater w ithdifferent chlorine concentrations. As little as

0.1 p pm continuous chlorination w ill producea positive shift in the corrosion potential,

significantly greater than the norm al shift thatoccurs even in the absence of chlorination.

Fortunately, chlorination also reduces the

cathodic current density in seaw ater, and so the

Figure 54 Effect of chlorination on the opencircuit potential of 254 SMO

stainless steel exposed in natural

seawater with and without continuous chlorination 44

0 10 20 30 40 50 6

P o t e n t i a l v s

A g / A g C

l ( m v )

Exposure Time (days)

1,000

800

600

400

200

0

-200

100 ppm0.2 ppm

0.1 ppm0 ppm

1 ppm Intermittent Chlorination

effect on corrosion is not as serious as m ight be

expected. B ecause stainless steel pitting andcrevice corrosion initiation potentials increase

w ith increasing chrom ium and m olybdenum ,and because of the cathode effect, the high-

perform ance stainless steels can give goodservice w here chlorination is necessary in

high chloride cooling w aters. Experience

has ind icated that the subgroup A -4 6%m olybdenum austenitic grades and the

subgroup s F-2 and F-3 ferritic g rades can beused w ith continuous chlorination in am bient

tem perature seaw ater at chlorine levels at leastas high as 1 p pm 45. The dup lex grades generally

seem to p rovide low er perform ance w ithinsim ilar P R E ranges. Interm ittent or targeted



chlorination w ill allow the use of considerably

higher chlorine levels 46. H igh tem perature andsevere crevices, such as those found at flanges,

w ill lim it the use of all but the m ost resistantgrades. Table 26 com pares 1 pp m chlorination

exposures at 15 °C (59 °F) and 40 °C (10 4°F). Forsevere service involving any o f these variables,

the subgroup A -6, 654 S M O stainless steel

eq uals the perform ance of the best nickel-basealloys and has seen extensive service as flange

connections in critical seaw ater handlingsystem s.

C hlorine and chlorine d ioxide p roduce highly

oxidizing co nditions in som e stages of thepaper pulp bleaching and w ashing process.

H ighly corrosive conditions are produced by

these oxidants acting in com bination w ithhigh ch loride ion residual, low pH , and high

tem peratures. Traditionally, Type 316 stainlesssteel had been used in som e o f the m ilder

co rrosive environm ents in the b leach plan t.H ow ever, trends tow ard w aste stream

closure and m ore advanced bleach and

environm entally friendly bleaching practiceshave produced m ore co rrosive cond itions.

These include higher chloride ion residuals andhigher tem peratures. C ond itions are m ost

severe in the D -stage, probab ly because itgenerally operates at the highest tem perature.

C orrosivity is also severe in the C - and C /D -stages b ecause these stages carry the highest

Condenser tubes in 654 SMO ®

stainless steel being installed in

a nuclear power plant.



C ond ensate and scrub bing liquo r w ill becom e

acidic w ith the S O 2 and also red ucing w ith S O 3

and H C l. The design and m ethod o f op eration

of the gas-handling system w ill also co ntribute

greatly to the severity of corrosive conditionsthat m ay d evelop. In general, raw cond ensate

and recycling w ill produce the m ost co rrosiveconditions, w hile w ashed w alls and

absorbent-treated liquors represent lesscorrosive conditions. The “generic FG D

system ”defined in A S TM S TP 837 50

describes the layout of a generic flue gas

desulphurization system w hich defines varioussystem locations in term s o f relative potential

for corrosion. This system is illustrated in Figure

56 , w here zo nes having different deg rees ofcorrosivity are indicated by the letter sym bols

A throug h H . Each zone is defined in term s ofboth qualitative and quantitative severity in

Tables 28 and 29 , respectively. From thestandpoint of m etallic co rrosion, the m ost

severe zones all involve d uctw ork and stacksor w et/dry cond itions w here the pH can be

<0.1 and tem peratures can be as high as182°C (360°F). Lo cations that are w ashed or

that hand le absorbent are m ild or m oderatelycorrosive.

The generic FG D system do es not account forchloride and fluoride levels, or any operating

variab les such as dep osit buildup or drains; sofurther inform ation is needed in order to m ake

Figure 56 Operating zones in a generic FGD system as defined in ASTM STP 837 50

Bypass Duct

CondensingFlow

Flood ZoneImpingement

Zone Hot Air ReheaterIn Line HeaterDirect Fire Heater

Packing

Stack

Wet/DryGasPassage

Alt.Path

DemistTrays

(if alt.)

Table 28 Qualitative description of scrubber operating zones 50

MechanicalCode Chemistry Environment Temperature

A Mild Corrosive (vapour) Mild MildB Moderate (Immersion) Mild MildC Moderate Moderate MildD Moderate Severe MildE Severe Mild ModerateF Severe Mild SevereG Severe Severe SevereH Moderate Severe Moderate

Table 27 Weld corrosion in a simulated D-stage paper bleach environment 49

Weld Parameters Corrosion Rate mm/yr (mpy)Name UNS Number Method Filler pH 6.5 pH 2.0

254 SMO S31254 – – 0.01 (0.4) 0.24 (9.0)254 SMO S31254 SMAW P12 0.10 (4.0)* 0.32 (13.0)**654 SMO S32654 – – <0.01 (0.4) 0.24 (9.0)

654 SMO S32654 GTAW – <0.01 (0.4) 0.25 (10.0)654 SMO S32654 GTAW P16 0.01 (0.4) 0.25 (10.0)654 SMO S32654 SMAW P16 0.04 (2.0) – Alloy C–276 N10276 – – 0.53 (21.0) 0.44 (17.0) Alloy C–276 N10276 GTAW C–276 0.53 (21.0) 0.44 (17.0)



judgm ents on m aterials selection. O ne of

the first and m ost broad ly based stud ies onstainless steel perform ance in FG D w as a test

rack exp osure p rogram conducted by theInternational N ickel C om pany 51 . In this

program , Types 316L and 317L w ere exposed

in a large num ber of com m ercial S O 2 scrubbingenvironm ents, w ith the results show n in Figures

57 and 58 . This w ork clearly show ed thestrong detrim ental effect of high chloride

and acidity, prim arily in term s o f increasingthe tendency for localized pitting or crevice

corrosion. N evertheless, in the early years ofFG D construction in the U .S .A ., a considerab le

num ber of ab sorbers and other “m oderate”

severity locations w ere co nstructed using eitherType 317L or a high m olybdenum version ofType 316L stainless steel. The aim w as to

operate these units at pH levels ab ove 4 and

chloride levels of not m ore than a few tho usandppm . A sum m ary of op erating experience w ith

these U .S . and E uropean units w as reportedby N iD I in 1989 in publication N o. 10 024, “The

U se of N ickel S tainless S teels and N ickel A lloysin Flue G as D esulphurization S ystem s in the

U nited S tates”and N o. 10 025, “Flue G asD esulphurization; the E uropean S cene”. W hile

m any of these installations w ere successful,operating exp erience sho w ed that m ore highly

alloyed stainless steels are needed in m oderateseverity locations w here chloride p lus fluoride

levels could som etim es range up w ard of 5,00 0

ppm , and n ickel-base alloys w ould benecessary for those severe locations handling

raw cond ensate at high tem perature.

The high-perform ance stainless steels as a

w hole have not been as extensively evaluatedas Types 316L and 317L, but they have

becom e preferred o ver high m olybdenumType 316 L and have been extensively used for

the “m oderate severity”locations in m anyrecent FG D installations. Investigators have

attem pted to quantify the p erform ance of thehigh-perform ance g rades based on the

behaviour of Types 316 L and 31 7L w ith

respect to ch loride and pH , and on relativepitting or crevice resistance as reflected by

the P R E num ber or C C T. The ap proxim atebehaviour of rep resen tative grad es is p resented

in Figure 59 . The exact position of each curvefor an individual grade is yet to be confirm ed

by field exp erience, but there is no question

that a w ide range in p erform ance and cost-effectiveness is available. A large num ber of

Table 29 Quantitative description of scrubber operating zones 50

MechanicalChemical Environment

Severity Environment (Abrasion Level) Temperature

Mild pH 3.8 Agitated Tk. Ambient toH2S04 Ducts, Thickener 66°C (150°F)

Moderate pH 0.1-3, 8-13.9 Spray Zone Ambient toH2S04 0-15% Tank Bottoms 93°C (200°F)

Severe pH <0.1, >13.9 Hi Energy Venturi Ambient toH2S04 15% Impingement- 182°C (360°F)

Turning Vanes Targets



31 7LM and 3 17 LM N absorber installationsw ith p H of ab out 4 and chloride up to several

thousand pp m w ere m ade beg inning in the1980s. These tw o g rades appear to b e

perform ing w ell under these m oderatecond itions and have the advantage of adding a

relatively sm all cost prem ium over the standardstainless steel grades.

W hen ch loride levels in the absorber beg in

to exceed about 5,00 0 ppm , concern arises

over the suitab ility o f 317LM N in this kind ofap plication. In such cases, the subgroup s A -4,

A -6, D -3, and D -4 austenitic and dup lexstainless steels are good cand idates and have

been used in a lim ited num ber of cases. Adisad vantage of these grad es, as w ell as

nickel-base alloys, for these m ore severe

applications is their relatively high costco m pared w ith nonm etallic lining, FR P, oracid-resistant brick. H ow ever, these g rades

have been very successfully used in the formof clad plate or w allpaper construction. Life

cycle cost com parisons sho w that this type of

co nstruction can provide substantially low eroverall co sts than rubber-lined carbon steel for

ab sorber ap plications w ithout the m aintenancepatch ing and rep air inheren t w ith rubber

linings. The result of a typ ical life cycle costanalysis is show n in Figure 60 . M ethods for

the q uality fabrication of clad plate andw allpaper designs have been develop ed and

are availab le from such sources as the N ickelD evelopm ent Institute and N A C E International

(see A ppendix 1).

The localized corrosion pred ictions as a

function of ch loride and pH in Figure 59 should

no t be used to estim ate p erform ance for thevery severe cond ition o f raw acid condensatethat m ay occur in d ucting and stacks. W hen

the pH beg ins to fall below ab out 1.0, thecorrosion m ode for m ost stainless steels,

includ ing the high-perform ance grad es, beg insto shift tow ard general attack. C orrosion data

for acid so lutions are m ore applicable for theseco nditions. G eneral experience has indicated

that only the m ost highly alloyed nickel-base

Figure 59 Approximate service limits for stainless steels and nickel-base alloys in flue gas condensates and acid brines at moderate temperatures [60-80°C (140-176°F)] 51,52,53

C h l o r i d e I o n C o n c e n t r a t

i o n ( p p m )

tempSf466 m nhbegins


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Figure 60 Life cycle cost comparisons for alloy clad and lined carbon steel absorbers 54

Gas Flow Rate (ACFM)

L i f e C y c l e

C o s t

( A C F M )

2 0 0

, 0 0 0

3 0 0

, 0 0 0

4 0 0

, 0 0 0

5 0 0

, 0 0 0

6 0 0

, 0 0 0

Stainless Steels

Low Mo Nickel Base Alloys

High Mo Nickel Base Alloys

Lined Carbon Steel

30

25

20

15

10

5

L i f e C y cl e C o s t ( A CF M

)

30

25

20

15

10

5

alloys w ill be useful in ducting or stacks w hereraw acid condensate is likely to form . A n

exception m ay be the new est subgroup A -6,the austenitic high-perform ance stainless steels

w hich have outstanding resistance to strongacids containing ch loride. A n exam ple of this

perform ance is provided in Table 30 w hich

gives the results of test rack exp osure inthe quench section of a m unicipal w aste

incinerator w here q uench liquo r pH w as 0 .5-1.0 and contained very high levels o f ch loride

and fluoride ions. The 654 S M O stainless steelin subgroup A -6 p erform ed at least as w ell as

several nickel-base alloys tested at the sam etim e. The disadvantag e of titanium in strong

fluoride-co ntaining acids w as also confirm edby these tests.

STRESSCORROSIONCRACKING

S tress corrosion cracking in stainless steels,w hen it occurs, usually involves either

anodically co ntrolled cracking in the p resence

of a sp ecific ion, usually chloride, orcathodically controlled hydrogen cracking.H alides other than chloride w ill also produce

cracking, but they are less often enco untered

and their effect w ill depend on other solutionvariables such as acidity and oxidizing

potential, just as w ith pitting and crevicecorrosion. The influence o f cations in halogen

salts is prim arily through their effect on the pHof hydrolization, the m ore acid salts b eing m ore

aggressive. S odium chloride, althoug h by farthe m ost co m m only encountered salt, is fairly

neutral; thus, it w ill generally be less aggressivethan salts containing calcium and m agnesium

ions. H ydrogen cracking usually req uires highhydrogen partial pressures and is confined

prim arily to the ferritic phase found in the

duplex and ferritic grades.

A s a fam ily, the high-perform ance stainlesssteels, regardless of structure type, generally

offer better stress corrosion cracking resistancethan the standard austenitic stainless steels.

The reason for this is that the 8 to 12 percentnickel in Types 304 and 316 stainless steel

is at an inopportune level from the standpointof stress corrosion cracking; this w as

dem onstrated m any years ago by C opson 56 ,using the b oiling 45% M gC l 2 solution. H igher

nickel, chrom ium , and m olybd enum increase

the stress corrosion cracking resistance ofaustenite, thereby im proving resistance in the

high-perform ance grad es. The ferrite p hasefurther im proves the resistance of the duplex

grades, and provides very good resistancefor the ferritic grad es in the co m m only

encountered chloride environm ents.Furtherm ore, it has recently becom e clear that

the boiling 45% M gC l 2 so lution, w hile clearlyshow ing alloying effects, is an extrem ely


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AL-6XN ® tower packing in

a distillation column

Table 30 Corrosion of welded coupons in a waste incineration plant flue gas quencher 55

UNS Weight Loss Crevice Corrosion PittingName Number mg/m2hr (mg/ft2hr) mm (in.) Corrosion

904 N08904 58 (5.39) 40 sites - 0.65 (0.026) in weld - 0.75 (0.030)2507 S32750 3 (0.28) 10 sites - 0.22 (0.009) in weld - 0.60 (0.024)254 SMO S31254 1 (0.09) 5 sites - 0.37 (0.015) 0

654 SMO S32654 0 0 0625 N06625 0 2 sites - 0.01 (0.0004) 0 Alloy C-276 N10276 0 4 sites - <0.01 (0.0004) 0 Alloy C-22 N06022 0 3 sites - <0.01 (0.0004) 0Titanium Gr 2 R50400 892 (83) 0 severe uniform corrosion



aggressive environm ent that is not necessarily

useful in defining areas of applicability. P resentresearch has placed em phasis on p rocedures

that com e closer to sim ulating real co nditions.W hen testing in sodium chloride environm ents,

estab lished alloying effects are verified; inaddition, the possibility o f obtaining useful

resistance from the high-perform ance stainless

steels in aggressive environm ents is indicated .This is illustrated in Figure 61 w here very long

failure tim es, or im m unity, are dem onstrated foralloys w ithin the austenitic high-perform ance

stainless steel nickel content range in 26%N aC l at 20 0°C (39 2°F).

WATER AND BRINEENVIRONMENTS

The high-perform ance stainless steels havebeen evaluated for stress corrosion cracking

resistance in a large variety o f laboratory tests

involving the chloride ion. M any of these testsw ere originally developed to ap ply to severe

conditions in co oling w aters or brines thatcould lead to stress corrosion cracking in the

standard stainless steels. B y variation in testco nd itions, these p roduce a range in test

severity that allow s com parisons am ong the

different high p erform ance stainless steelsub group s and the standard stainless steelgrad es. The perform ance of the stainless steels

in these tests is sum m arized qualitatively in

Table 31 . The tests listed in this table have

been arranged w ith the m ore severe high

tem perature acid chloride environm ents onthe left side; the severe, high oxyg en, high

tem perature environm ents on the right side;and the m ore m od erate, low tem perature

environm ents in the centre. The grad esubgroups are listed in order of increasing

resistance in these environm ents from topto bottom in each section of the tab le. The

standard austen itic g rad es, as exem plified byType 316, w ill develop stress corrosion cracking

in all these tests. The m ost severe test, boiling45% M gC l2 w ill produce stress corrosion

cracking in all of the h igh-perform ance grades

except the low nickel ferritic g rades. In betw een

these extrem es of grade sensitivity and test

severity, there exists a w ide range in alloyperform ance.

O f the high perform ance austenitic grad es, the

stainless steels in subgroup A -2 show stresscracking susceptibility in all of these tests,

and the sub group A -5 stainless steels are

only m arginally better. W hile both of thesesubgroup s w ould prob ably perform som ew hat

better than Type 3 16 in less severe tests, theyshould no t be considered as solutions to stress

cracking prob lem s encountered w ith Type 31 6because their nickel content is only slightly

higher than that of Typ e 316. It is w ith therem aining austenitic subgroups, w hich have

nickel co nten ts above 1 8 percent, that stresscorrosion cracking resistance is d ram atically

im proved. This im provem ent increases w ithincreasing nickel co ntent and w ith increasing

chrom ium and m olybdenum . For exam ple, of

the high p erform ance austenitic stainless steels,904L and 20 C b-3 have frequently been used in

applications w here Type 31 6 w ould beconsidered inadequate

from the standpointof stress corrosion

cracking , and they have

given g ood service inthese instances. Table

31 suggests that the A -4

and A -6 grades shouldbe useful in even m ore

aggressive environm ents.

The d up lex high-perform ance stainless

steels are superior instress corrosion cracking

resistance com paredw ith Types 304 and 316

because they containthe ferrite phase, but

they do no t have theability to resist extrem ely

aggressive environm entsas do the m ost highly

alloyed austenitic and

ferritic alloys. This is

Figure 61 Relative severity of the NaCl and MgCl 2 tests inevaluating the effect of

nickel on the stresscorrosion resistance of stainless steels 57

T i m e

t o C r a c

k i n g ( h )

1,000

100

10

10 10 20 30 40 50 60 70

Ni (wt.%)

26% NaCI200˚C

45% MgCI2

155˚C



AUSTENITIC STAINLESS STEELS



Table 31 Comparison of stress corrosion cracking resistance of stainless steel groups in accelerated laboratory tests

600 ppm Cl 100 ppm Cl42% MgCl2 35% MgCl2 Drop Evap. Wick Test 33% LiCl2 40% 25-28% NaCl 26% NaCl 26% NaCl (NaCl) (sea salt+02)

Typical boiling boiling 0.1M NaCl 1500 ppm Cl boiling CaCl2 boiling autoclave autoclave autoclave autoclaveGrade Alloy 154°C 125°C 120°C as NaCl 120°C 100°C 106°C 155°C 200°C 300°C 230°C GroupName Content U-Bend U-Bend 0.9xY.S. 100°C U-Bend 0.9xY.S. U-Bend U-Bend U-Bend U-Bend U-Bend No.

16 - 20 CrType 316L 10 -15 Ni

2 - 4 Mo

17 - 20 Cr317LMN 11 - 17 Ni

3 - 5 Mo

23 - 26 CrMn-N Alloys 12 - 18 Ni

3 - 5 Mo

19 - 26 Cr904L 21 - 30 Ni

3 - 5 Mo

19 - 26 Cr Alloy 20 32 - 46 Ni

2 - 4 Mo

19 - 25 Cr6Mo Alloys 17 - 26 Ni

5 - 7 Mo

24 - 28 Cr654 SMO 21 - 32 Ni

6 - 8 Mo

18 - 26 Cr3RE60 3 - 5 Ni

0 - 3 Mo

21 - 26 Cr2205 2 - 7 Ni

2 - 4 Mo

24 - 27 Cr255 4 - 8 Ni

3 - 4 Mo

24 - 26 Cr2507 6 - 8 Ni

3 - 5 Mo

18-20 Cr444 0-0.5 Ni

1-3 Mo

25-27 CrE-BRITE 26-10-0.3 Ni

0.75-1.5 Mo

25-30 CrSEA-CURE 1-4 Ni

3-4.5 Mo

28-30 Cr AL 29-4-2 2-2.5 Ni

3.5-4.2 Mo

A - 2

A - 5

A - 3

A - 1

A - 4

A - 6

D - 2

D - 3

D - 4

F - 1

F - 3

F - 4

Cracking Anticipated Cracking Possible Cracking Not Anticipated Insufficient Data



probab ly because their nickel co ntents, at 2

to 8 percent, are at about the sam e level thatis highly d etrim ental in the austenite phase.

The ferritic g rades all have good chloridestress corrosion cracking resistance. Those that

contain no nickel do not show susceptibility inany of the test environm ents show n in Table

31 , w hile the 1 to 4 percent nickel found in the

m ore highly alloyed F-2 and F-3 grades causessuscep tibility in the m ore severe environm ents.

The application of laboratory stress corrosion

cracking data to engineering design is verydifficult because m any system variab les other

than alloy conten t are involved. These includethe actual stress pattern; the possibility o f

evaporation and localized ion concentration;and the potential, w hich is d eterm ined by the

am ount of oxygen availab le. H eat exchang erssubject to localized boiling and hot surfaces

covered w ith insulation are w idely encountered

situations involving these factors. Thelim itations of the standard stainless steel grades

m ay ind icate the need for high-perform ancestainless steel in these instances. The W ick

Test and D rop Evaporation Test both attem ptto sim ulate these situations 58, 59 . The D rop

Evaporation Test is perhaps the m ore severe o f

the tw o tests and is often cond ucted over arange of stress levels. This test can provideguidance for grade selection in m any cases.

Figure 62 gives d ata for a rep resentative groupof high-perform ance stainless steels evaluated

by the D rop Evaporation Test; all tests w ere

cond ucted at the sam e laboratory underexactly the sam e test co nd itions. These data

suggest that the ferritic grades, as w ell as thehigher alloyed austen itic and duplex high-

perform ance stainless steel subgroup s, shouldperform w ell in situations of localized boiling

and evaporation that are encountered in m anycooling w ater applications w ith boiling

tem peratures associated w ith near-am bientpressures.

A ctual field experience supports these

conclusions. There have b een m any instances

of the successful use of high-perform ance

stainless steels to rep lace Typ es 304 and 316

heat exchanger tubing, piping , and vesselsthat failed due to stress corrosion cracking.

Incidents of stress corrosion cracking w iththese rep lacem ent grades have been

exceedingly rare. A lthough lim its of usefulnessare difficult to define, the laboratory and field

data p rovide som e guidance for the case of

oxygen-containing cooling w aters as show n in

Figure 63 . The so lid curve for Types 3 04 and

316 is based on a survey of operating heatexchangers and describes the tem perature and

chloride lim its for useful service extending toabout six years. This curve w ill shift slightly

depending on variab les such as the typeof heat exchanger and the p rocess fluid

tem perature, but it provides a guide for Types304 and 316 and em phasizes that stress

corrosion cracking, w hile it can o ccur atlow er tem peratures, becom es quite likely at

tem peratures above ab out 50°C (120°F) if

evap oration o ccurs even at very low w aterchloride co ntents. The curves for the high-

perform ance stainless steels are based onthe laboratory test data from Figure 62 and

field experience. These curves show thatthe high-perform ance stainless steels are

useful at significantly higher w ater chloride

concentrations and tem peratures.

SOUR OIL AND GASENVIRONMENTS

The p resence of hydrog en sulphide adds to the

co rrosiveness o f high chloride w aters ofteninvolved w ith o il and gas production, and the

presence o f carbon d ioxide o r intentionallyad ded acidifiers increases the aggressiveness

of these environm ents. This increases thelikelihood for pitting or crevice corrosion, stress

corrosion cracking, and even general co rrosionas the severity of the environm ent increases. A t

relatively low levels of H 2S , the standard grad esof all three structure types can provide useful

resistance and m any are includ ed in the N A C ES tandard M R 0175, “S ulphide S tress C racking

R esistan t M etallic M aterials for O ilfield

Equipm ent.”H ow ever, as H 2S partial pressure,

ch loride co ncentration,

tem perature, and acidityincrease, the high-

perform ance austen iticand duplex stainless

steels are necessary toprovide useful resistance.

The high perform ance

austenitic grades w illgenerally ou tperform

the duplex grad es fromthe standpoint of H 2S -

assisted stress corrosioncracking w hile the

ferritic grades w ould bevastly inferior to both.

B ecause m any of theseapplications require high-

strength, the duplexgrad es are often prim e



candidates for applications involvingenvironm ents of m oderate severity and they

have been studied extensively to define theirlim its o f serviceability in these circum stances.

The resistance of duplex stainless steels

to sour environm ents is a very com plex

sub ject because resistance depends on

interrelationships betw een m etallurgical,environm ental, and stress factors. In thepresence of H 2S , the prim ary failure m ode is

hydrogen stress cracking of the ferrite phase.Low pH and high chloride contents seem to

accelerate this p rocess. H ow ever, the effectof tem perature is such that susceptibility

increases as tem perature increases fromam bient to abou t 10 0°C (21 0°F) and then

declines at higher tem peratures. The anodic

stress corrosion cracking m echanism orgeneral co rrosion can take over at higher

tem peratures, esp ecially if the chlorideco ncentration is high. From a m etallurgical

standpoint, hydrogen cracking w ill be favouredif the structure is high in ferrite, w hile excessive

austenite w ill prom ote the anodic form ofcracking . C old w ork w ill prom ote b oth form s

of cracking , but som e d egree of cold w ork isoften em ployed to provide h igher strength. In

addition to the environm ental factors alreadym entioned , the p resence o f oil, w hich coats

m etallic surfaces, can provide an inhibitingeffect; and certain ions, such as bicarbonate

in seaw ater and produced w ater, raise the pHand produce less severe cond itions than

those in a laboratory using unbuffered sodiumchloride. The m etho d of stressing specim ens

in laboratory tests also produces differing testresults that m ust be interpreted for applicability

to engineering situations.

M any laboratory test prog ram s seem to

have produced overly conservative resu ltsin co m parison to service exp erience. For

exam ple, stress corrosion cracking evaluationsconducted w ith the slow strain rate test (SS R T)

generally define low er acceptab le H 2S levels

than tests cond ucted using other m ethods.This difference and the influence of H 2S andtem perature on stress corrosion cracking are

illustrated in Figure 64 . The SS R T test usuallyproduces cracking at the low est H 2S partial

pressures and a m axim um in stress corrosion

cracking susceptibility at ab out 100°C (210°F) is

Figure 62 Stress corrosion in the dropevaporation test with sodiumchloride solution at 120°C (248°F)

showing the stress at whichcracking will initiate 59

P e r c e n t o f

2 0 0 ˚ C / 3 9 2 ˚ F Y i e l d S t r e n g t h

120

100

80

60

40

20

0Type 316 2205 2507 904L 254 SMO 654 SMO

Figure 63 Stress corrosion in cooling waters based on actual experience withType 304 and Type 316 and

predictions for high-performance stainless steels based on laboratory tests 60

˚F 32 212 392 572 7˚C 0 100 200 300 40

C h l o r i d e I o n C o n c e n t r a

t i o n ( p p m )

Temperature

10,000

1,000

100

10

1

A-5, D-1, D-2

A-1, A-4 A-6, D-3

No Stress Corrosion

Stress Corrosion

Type 316Type 304



ind icated . Efforts have been m ad e to definethe H 2S and tem perature regim es in w hich

the various failure m odes w ill be operative. A nexam ple for 2205 is given in Figure 65 . A bove

som e m inim um com bination of H 2S andtem perature, localized pitting becom es a

possibility follow ed by stress corrosion cracking.At the highest com binations of H 2S and

tem perature, general co rrosion is encountered .These reg im es w ill shift w ith other environm ental

factors as w ell as alloy com position and grad e.

This is show n for m artensitic, duplex, andaustenitic grades in Figure 66 . D uplex stainless

steels perform w ell at interm ediate conditions,but the high-perform ance austenitic stainless

steels o r nickel-base alloys are required forsevere service.

HYDROGEN ENVIRONMENTS

The standard and high-perform ance austenitic

stainless steels are very resistant toenvironm ents having high hydrogen partial

pressures and are often specified for handling

hydrog en over a w ide range of tem peraturesand pressures. The ferrite phase is suscep tible

to hyd rogen dam age, reflected in poorerperform ance in the duplex and especially the

ferritic stainless steels. The duplex grades canretain so m e ductility and toug hness und er

m oderate hyd rogen charging cond itionsbecause the austenite w ill provide residual

ductility even if the ferrite is severely em brittled.

This beneficial effect of austenite is notavailable in the ferritic grades; therefore,

caution m ust be exercised w hen considering

them for ap plications involving hydrogen . For

exam ple, ferritic grad es can develop voids andcracks w hen exposed to hydrog en-containingannealing atm osp heres. H ydrog en charging

is a lso a possibility at the m ore m oderatetem peratures involved in hydrocarbon

processing, especially if a hydrogen chargingcatalyst such as cyanide is p resent. W ith heat

exchangers handling cooling w aters, it ispossible to charge hydrog en and prod uce

severe em brittlem ent if the surface is

m aintained cathodic b y galvanic coupling orcathodic protection. The poten tial at w hich

charging beg ins to becom e significant is about-800 m V com pared w ith the standard calom el

electrode. W ater chloride co ncentration,biological activity, potential, tem perature,

and tim e all affect the severity of hydrogencharging. The effect of chloride on the loss of

ductility o f a subgroup F-2 ferritic grade due to

hyd rogen em brittlem ent is show n in Figure 67 .

H ydrogen em brittlem ent red uces d uctility andtoughness. Fracture is usually by cleavage,but severe em brittlem ent w ill even produce

grain boundary fracture. S tabilization w ithtitanium or alloying w ith nickel seem to

ag gravate the effect. H igh-purity E-B R ITE 26-1is p robab ly the m ost resistan t of the high-

perform ance ferritic grad es and has g ivengood service in m any refinery ap plications

invo lving both hyd rogen and cyanides.

Figure 64 Hydrogen stress corrosion of duplex stainless steels showing variability in test results for different test methods in NaCl-CO 2-H 2S 61

˚F 32 122 212 302 392 482 572˚C 0 50 100 150 200 250 300

H y d r o g e n

S u l p h i d e

P a r t i a l P r e s s u r e

( b a r )

Temperature1: Tensile 5-15% NaCI, 70 bar CO2 (29)

2: SSRT 20% NaCI, 25 bar CO2(29)

3: U-bends 10% NaCI, 50 bar CO2 (30)

4: 4pt bends 20% NaCI, 25 bar CO2 @YS


6: U-bends 5% NaCI, 30 bar CO2(31)

7: U-bends, C-rings & 4pt bends 10NaCI, 30 bar CO2 (19)


10.000

1.000

0.100

0.010

0.001

736

4

1

5 82

No Stress Corrosion

Stress Corrosion



Figure 66 Proposed applicability range for corrosion resistant stainless steels

in sour environments containing 50 g/l NaCl 63

˚F 32 122 212 302 392 482 572 662˚C 0 50 100 150 200 250 300 350

H y d r o g e n

S u l p

h i d e P r e s s u r e

( b a r )

Temperature

1.000

0.100

0.010

0.001

25Cr Duplex 75-125 ksi

Duplex 22-25Cr 140 ksi

22Cr Duplex 75-125 ksi

13Cr


Figure 65 Corrosion of duplex stainless steels in 20% NaCl-H 2S environments based on electrochemical prediction and experimental results 62

0.01 0.10 1.00 10.00


( ˚ C ) T em

p er a t ur e ( ˚ F )

Hydrogen Sulphide Pressure (MPa)

350

300

250

200

150

100

50

0

662

572

482

392

302

212

122

32

StressCorrosion

NoStress

Corrosion

Active GeneralCorrosion

LocalizedCorrosion

NoCorrosion

Figure 67 Loss of bend ductility from hydrogen after cathodic charging in sodium chloride solutionsfor S44660 high-performanceferritic stainless steel 64

1 10 100 1,000 10,00

P o t e n t i a l ( V o

l t s v s .

S C E )

Time (hours)

-1.2

-1.1

-1.0

-0.9

-0.8

-0.7

-0.6

No BendTest Failure

Bend TestFailure

5 0 p p m C h l o r i d e

1 , 0 0 0 p p m C h l o r i d e

1 8 , 0 0 0 p p m C h l o

r i d e



does deal sp ecifically w ith intergranular attack.

This standard w as originally designed toevaluate susceptibility to intergranular attack

of nickel-rich, chrom ium -bearing alloys, butnow it includes a lim ited num ber of the high-

perform ance austenitic g rades. W hether it isbroadly applicable to all of these grades is

unknow n, and there is the possibility that the

G 28, M ethod A m ay not be ad equatelysensitive to intergranular attack susceptibility as

has b een reported by Q varfort 8. H e hasproposed that a constan t-poten tial etch ing

m ethod (C P E) w ill have very high sensitivity fordetecting sensitization and m ight be useful for

acceptance testing.

The evaluation of susceptibility to intergranular

attack has received serious attention o nly forthe high-perform ance ferritic grades. This is

undoub ted ly due to the fact that som e ofthese steels are extrem ely sensitive to the

effect of cooling rate on intergranular attack.A S TM A 76 3 addresses intergranular attack

and includ es m ost of the high-perform ance

ferritic grades, and it provides for detectingthe effects o f carbide, nitride and interm etallic

phases, depend ing on w hich test m ethodis used.

C ontaining both ferrite and austenite, the

duplex alloys p resen t a challenge for any



sing le approach to an

acceptance test, and sothe new A S TM S tandard

Test M ethod A 923 hasbeen created . It uses

three distinctly differenttests as a basis for

determ ining acceptability,

w hich is d efined as theab sence o f detrim ental

interm etallic phases:1. Test M ethod A -

S od iumH ydroxide E tch

Test of theC lassification of

Etch S tructures2. Test M ethod B -

C harpy Im pactTest for

C lassification of

S tructures3. Test M ethod C -

Ferric C hlorideC orrosion Test for

C lassification ofS tructures.

FABRICATION

W ell-established principles w hich apply to thefabrication of the standard stainless steel

grad es apply eq ually to the high-perform ancegrad es and provide a good starting point for

understanding their special req uirem ents.Virtually all fabrication techniques applied to

the standard grad es also ap ply to the high-

perform ance grad es. D ifferences includ e:1. m ore critical ho t w orking and annealing

tem perature ranges associated w ithsecond ary phase form ation

2. m ore critical co oling rate req uirem entsassociated w ith second ary phase

precipitation kinetics

3. m aintenance of structure and corrosion

balance after w elding4. higher strengths w hich affect m any co ld

w orking and m achining operations5. avoidance of surface contam ination

through all stages o f fabrication.

S uccessful fab rication req uires a goodm etallurgical understanding of the sp ecific

grade of stainless steel and close attention toall details of fabrication, especially for the

duplex stainless steels. The best inform ationan d guidance on fab rication of individual

grad es are o btained from the producer. Thebroad overview discussed here highlights the

m ost im portant principles and considerationsof fabrication o f the high-perform ance

stainless steels.

HOT WORKING

The three high perform ance stainless steel

fam ilies d isp lay distinct differences in hotw orking behaviour w hich result directly from

the different characteristics o f the ferriteand austenite.

The austenitic high-perform ance stainless

steels disp lay good hot ductility, but over a fairly

narrow tem perature range ( Figure 68 ). Therapid red uction of ductility above ab out 1200°C(2200°F) results from the deleterious g rain

bound ary effects o f sulphur, oxygen, and

pho sphorous. P roducers m ake special effortsto m inim ize and neutralize these im purities

during m elting and refining of the steel; w hilehelpful, this does no t co m pletely com pensate

for these effects. Increased nitrogen conten tand low self-diffusion rates of the austenite

also reduce high strain rate ductility at low ertem peratures. B ecause they are p rone to

segregation and sigm a p hase form ation in theas-cast condition, it is desirable to w ork the

austen itic stainless steels above the uppersigm a phase so lvus tem perature. Therefore,

ho t w orking m ust be cond ucted over a rather

narrow tem perature range. These grades alsooxidize rapidly at high tem peratures. Increasing

m olybdenum increases this oxidation tendency;

A S TM A 923 is based on the p rop ositionthat interm etallic p hases have an effect on

corrosion resistance and toughness; and thatdetection o f these p hases above som e lim it

can provide for distinguishing acceptab lem aterial. A lthough not stated exp licitly, the

interm etallic p hase involved is prim arily sigm aphase, and possibly chi or laves phase for

M ethods B and C . N one of the m ethods hasbeen dem onstrated to d etect sm all am ounts of

carbide o r nitride that could have an effect on

intergranular attack. A S TM A 923 is intendedsp ecifically for m ill products and is not a

fitness-for-service test. U se of this o r any otherstandardized acceptance test as a fitness-for-

service test m ay be p ossible, but only after thetest environm ent has been sho w n to correlate

w ith intended service conditions. U se of its test

procedures for qualification o f w elds m ay b epossible, but the accep tance criteria in A 923,developed to b e applicable to annealed m ill

products, are not ap plicable to w eldm ents. A tthe tim e of this w riting (2000), A 923 includes

only duplex grades S 31803 and S 32205 and

provides acceptance criteria for both. It isanticipated that other high perform ance dup lex

stainless steels w ill be added because of theinterest in having som e accep tance criteria for

this alloy fam ily.



so the upper tem perature and tim e lim it for

heating and ho t w orking is a com prom isebetw een excessive oxidation and the tim e

needed to accom plish hom og enization.

Ferrite is relatively w eak, has high self-diffusion

rates, and has a high so lubility for suchim purities as sulphur and phosphorus.

Thus, the ferritic grad es have very good ho tw orkability over a w ider tem perature range

than the austen itic g rad es ( Figure 68 ). Thelow er-tem perature w orking lim it is determ ined

prim arily by the up per tem perature o f sigm aphase form ation, w hile excessive scaling

determ ines the upper tem perature lim it.The ferritic stainless steels have little tendency

for as-cast seg regation; so there usually islittle need for the long so aking tim e that is

required w ith the austenitic grades to

m inim ize seg regation.

The d up lex stainless steels co m bine thebest and the w orst of the hot w orkability

characteristics of their com ponent phases.

U nlike the single phase grades, the relativeferrite-austenite b alance o f the d uplex stainless

steels changes dram atically as tem peratureincreases above abou t 11 00 °C (20 00 °F). H ot

w orkability is poor at low tem peratures becausethe steel contains the m axim um proportion of

austen ite. This austen ite is m uch stronger thanferrite at these tem peratures; so m ost of the

ho t w orking deform ation is ab sorbed by theferrite, w hich cannot accom m odate it on a

m acroscopic level. A t high tem peratures, thestructure b ecom es pred om inately ferritic and

the steel disp lays w orkability sim ilar to that of

the ferritic g rades. Therefore, high w orkingtem peratures are p referred , and tem perature

is lim ited only b y the point at w hich oxidationbeco m es excessive.

COLD WORKING

The m ain consideration w hen cold w orking the

high-perform ance stainless steels is their higherstrengths co m pared w ith the standard stainless

steel grades. This w ill have an effect on form ing

eq uipm ent load ing, pow er, and lubrication

requirem ents. These g rades can b esuccessfully cold w orked by all co nventionalm ethods, bu t dem and s on equipm ent w ill be

substantial. The three fam ilies of stainless steelsbehave som ew hat differen tly because the ferrite

phase has an initial high yield strength andinitial high w ork hardening rate, w hile the

austenite phase disp lays greater ductility anddevelops greater w ork hardening w ith heavy

co ld red uctions. These differences am ong

grades are illustrated in Figure 69 , w here yieldstrength and ductility are show n as a function

of co ld red uction. The d uplex grad es exhibitthe initial high strength and w ork hardening

characteristics of the ferrite phase, w hichm akes them very stiff w hen rolling or bending .

This effect is not as noticeable w ith theaustenitic grades until very heavy cold

reductions are encountered . B ecause theductility o f the high-perform ance ferritic and

Figure 68 Hot ductility of wrought standard and high- performance stainless steels by structure type

˚F 1652 1742 1832 1922 2012 2102 2192 2282 2372˚C 900 950 1,000 1,050 1,100 1,150 1,200 1,250 1,300

R e d u c t i o n o f

A r e a

( % )

Temperature

100

90

80

70

60

50

40

30

20

Type 316Austenitic

18Cr-2MoFerritic 2205

Duplex

High-Performance

Austenitic



duplex grades is less than that of the austenitic

grad es, it can becom e a lim iting factor at heavyred uctions. W ith cutting operations such as

shearing and blanking, the usual req uirem entfor sharp blad es and proper clearances is

esp ecially im portant w ith these stainless steels.A lso, because of their high strengths, m ore

springback w ill often be enco untered in

operations such as bending. D etailedinform ation on the co ld w orking of stainless

steels can be found in the N iD I publicationN o. 428, “Fabrication o f C hrom ium -N ickel

S tainless S teel (300 S eries)”.

ANNEALING

The m ost im portant considerations w henannealing the high perform ance stainless

steels are:1. furnace atm osp heres and possible surface

co ntam ination

2.avoiding second ary phase form ation3. re-solutionizing precipitates and reducing

segreg ation4.cooling rate

5.potential loss of chrom ium from surfaces.

Transform ation diagram s should be consu lted

w hen selecting tem peratures and coolingrates. W hile m ost diagram s are based o niso therm al transform ation kinetics, exp erience

has show n that continuous co oling results inslow er kinetics. Therefore, tim e lim its based

on isotherm al diagram s are usually som ew hat

co nservative w hen d efining the m inim umallow ab le cooling rate to avoid seco ndary

phase form ation. W hile interm etalliccom po und s m ust be avoided b ecause o f their

ad verse effects on m echanical and co rrosionproperties, carbide and nitride precipitation

can be very rapid, significantly reducingco rrosion resistance but producing no

noticeab le effect on m echan ical properties.A s w ith heating for hot w orking, there are

significant differences in annealing principlesand concerns am on g the three fam ilies o f

high-perform ance stainless steel.

The austenitic stainless steels are tolerant ofnitrogen-containing annealing atm ospheres, but

no t of atm ospheres having carburizing potentialbecause it is desirab le to m aintain the carbon

co ntent at less than 0.02 percent in thesem aterials. These g rad es req uire higher

annealing tem peratures than the ferritic and

duplex stainless steels because of their highsigm a and chi phase solvus tem peratures. It is

desirab le to anneal at high tem peratures tom inim ize segregation, but this increases the

likelihood of rapid oxidation and loss of

chrom ium from surfaces. The annealingtem perature range is relatively narrow andrepresents a com prom ise am ong com peting

factors. All the austenitic grades require rapidcooling after annealing to avoid a loss in

corrosion resistance associated w ith second aryphase precipitation.

The annealing atm osphere is extrem elyim portant w ith the ferritic grades. They

Figure 69 Effect of cold work on the strength and ductility of high-performance stainless steel familiescompared with Type 316 stainless steel

0 10 20 30 40 50 60 70

Y i e l d S t r e n g t h ( 0 . 2 %

, M P a )

Yi el d


Cold Reduction (%)

E l on g

a t i on ( % )

1,300

1,200

1,100

1,000

900

800

700

600

500

400

300

200

100

0

190

174

160

145

130

116

101

87

73

58

4429

15

0

90

60

30

High-Performance AusteniticHigh-Performance DuplexHigh-Performance FerriticType 316



tem peratures o r long annealing tim es b ecause

all reactions are very rapid at high tem perature.W ith the exception of A L 29-4-2, the ferritic

grad es all use stab ilizing elem ents such astitanium or niobium for carbon and nitrogen.

A nnealing should be carried out at a lowenough tem perature to ensure that carbon is

effectively stabilized by com bining w ith these

elem ents. A s w ith all the high-perform ancestainless steels, annealing conditions and

cooling rates after annealing should take intoco nsideration w hether the m aterial being

annealed has been w elded , or is m erely beingannealed to rem ove the effects of cold w ork.

Ferritic alloys are produced in thin sections; soair or fan cooling can be adequate w hen no t

dealing w ith w elds. W elds usually w ill deliveradequate p erform ance in the as-w elded

condition; ho w ever, cooling rates m ust bevery rapid if they are annealed.

The annealing atm osp heres used w ith d up lexstainless steels can have som e nitriding

poten tial, but they should not be carburizing orcapable of hydriding. There usually is little need

to use extrem ely high tem peratures to dissolve

precipitates o r rem ove seg reg ation, and

extrem ely high tem peratures sho uld be avoidedto lim it excessive ferrite in the final structure

and loss of chrom ium from the surface. Theannealing tem perature range usually beg ins

above the carbide and sigm a solvustem peratures and extends upw ard to the

tem perature that prod uces a m axim um of

ab out 60 percent ferrite. B ecause these g rad esare not stab ilized w ith respect to carbon and

nitrogen, cooling rates m ust be rap id enoughto avoid sensitization by these e lem ents. The

possibility of sensitization increases as theam ount of ferrite increases; therefore, the

anticipated am ount of ferrite existing over thecarbide precipitation range should be

considered w hen determ ining the cooling rate.R ap id sigm a precipitation over the tem perature

reg ion near the nose of the transform ationcurve is usually the m ost troubleso m e aspect

of co oling after annealing or w elding. H eat

com positions having high nitrogen arepreferred w here heavy sections or other

difficult circum stances exist becausenitrogen significantly delays the start of

this transform ation.

Vent piping

for pharmaceutical

manufacturing in

654 SMO ®

have high so lubility

and diffusivity for suchim purities as carbon,

nitrogen, and hyd rogen.A tm ospheres should be

as neu tral as possiblew ith regard to these

elem ents, and surfaces

m ust be d egreasedbefore furnace charging,

especially in the case oftubes w hich m ay have

residues of draw inglubricants. A ir, argon, or

vacuum atm ospheres arepreferred for the ferritic

alloys. They d o no trequire excessively high



OPERATION HIGH SPEED TOOLING CARBIDE TOOLINGSpeed Feed Speed Feed

(sfm) (m/min.) (ipr) (mm/rev.) (sfm) (m/min.) (ipr) (mm/rev.)

TURNING - Rough 25 8 0.030 0.75 200 65 0.015 0.40TURNING - Finish 35 15 0.008 0.20 290 95 0.004 0.10DRILLING - 1/4 in. HSS, 3/4 in. C-2 25 8 0.004 0.10 70 25 0.006 0.15DRILLING - 1/2 in. HSS, 1-1/2 in. C-6 30 10 0.015 0.40 100 35 0.009 0.25TAPPING 15 5 – – – – – –THREADING 20 7 – – 290 95 – –BAND AND HACK SAWING - <1/2 in. thick 90 30 12 t/in. 0.50 t/mm – – – –BAND AND HACK SAWING - >1/2 in. thick 60 20 8 t/in. 0.30 t/mm – – – –

in./tooth mm/tooth in./tooth mm/toothMILLING - Face and Side - Rough 30 10 0.004 0.10 60 20 0.008 0.20MILLING - Face and Side - Finish 70 25 0.002 0.20 90 30 0.004 0.10MILLING - End - Rough 20 7 0.002 0.20 30 10 0.003 0.08MILLING - End - Finish 60 20 0.002 0.20 80 25 0.002 0.05

Table 32 Machining parameters for high-performance austenitic stainless steels 65

MACHINING

W hen ap propriate consideration is g iven to thesp ecial characteristics of the high-perform ance

stainless steels, they can be m achinedsuccessfully by all the m etho ds com m only used

to m achine the standard stainless steel and

nickel-base alloys. C om pared to the 300-seriesausten itic grad es, the high-perform ance

stainless steels have:1. higher roo m tem perature and elevated

tem perature strength2.higher w ork hardening rates

3. sim ilar galling characteristics4.extrem ely low sulphur co ntents.

A s a result, m achining w ill be m ore d ifficult thanw ith the standard grad es, and careful attention

m ust be given to detail to ensure success.

The b asic m achining principles that apply to the

standard stainless steel grad es and nickel-basealloys are a good starting point for m achining

the h igh-perform ance stainless steels. Theseinclude sharp tools, rigid setups, positive feeds,

ad equate dep ths o f cu t, positive cuttinggeo m etries w here possible, and quality tooling

and coolant designed for stainless steels. Feedrate and dep th of cu t are very im portant if

there w ill be a subsequent finishing operationbecause prior surface w ork hardening effects

m ust be rem oved as m uch as possible before

attem pting shallow er finishing passes. Finishingpasses should be as deep as possible to cut

below the w ork hardened surface layer. H ighcu tting tool toughness is helpful because of

the high strength of the stainless steel. H ighm achine pow er is also im portant because of

the high strength and high w ork hardeningbehaviour of these stainless steels. The

m achining param eters given in the N iD Ipublication N o. 11 008, “M achining N ickel

A lloys,”for the G roup C nickel-base alloys in

the annealed cond ition provide a good startingpoint for the high-perform ance stainless steels.

Table 32 , based on the ab ove pub lication, givesm achining param eters for som e b asic

operations.

O f the three stainless steel fam ilies, the

austen itic stainless steels are the m ost difficultto m achine. These grad es, esp ecially the m orehighly alloyed subgroup s, have m achining

characteristics sim ilar to the corrosion resistantnickel-base g rad es in the solution annealed

condition. The ferritic grades are the easiest to

m achine. M achining param eters that w ouldusually be used for Type 316 stainless steel can

provide a starting point for w orking w ith thehigh-perform ance ferritic stainless steels. The

dup lex grades are ab ou t halfw ay betw eenType 316 and the high-perform ance austenitic

grades.



WELDING

The high-perform ance stainless steels arew eldab le by m ost processes norm ally used for

the standard grad es; how ever, m uch g reaterattention to detail is needed to achieve

acceptab le results. The high-perform ance

stainless steels are m uch m ore sensitive tosm all m etallurgical variables and their typ icalsevere applications p ut high d em ands on the

co rrosion and m echan ical properties of thew elds. S uccessful w elding dem and s a good

m etallurgical understanding of the m aterial and

of the additional req uirem ents of w elding. A nexcellent guide for the w elding of all stainless

steels is N iD I publication N o. 11 007,“G uidelines for the W elded Fab rication of

N ickel-C ontaining S tainless S teels forC orrosion R esistant S ervices”. Literature

provided by m anufacturers is the best sourceof detailed w elding inform ation and should

alw ays b e consulted once a decision ism ad e to w ork w ith a sp ecific g rade. The

follow ing g uidelines p rovide an overview ofconsiderations that apply to all the high-

perform ance stainless steels.

M ost of the req uirem ents that ap ply to w elding

the standard grad es also ap ply to the high-perform ance stainless steels. These include:

1.avo idance of oxidation during w elding2. avoidance o f contam ination by carbon and

sulphur and, in som e cases, by nitrogen3. post-w eld rem oval of w eld oxide and heat

tint.These requirem ents are stricter than they are

for the standard grad es. P rim ary additionalrequirem ents relate to the therm al cycle

because of the possibility of second ary phase

form ation, and the choice of filler m etalbecause of its influence on corrosion resistance

and m echanical properties. C ontrol of w eldm etal ferrite is less im portant in the high-

perform ance grades than in the standardaustenitic grad es. The high-perform ance

austenitic stainless steels and their filler m etalsare d esigned to be fully austenitic at all

tem peratures beg inn ing just below the solidustem perature. W hile not helpful to hot cracking

resistance, the fully austenitic structure reducesthe form ation of sigm a phase, w hich can form

rapidly w ithin ferrite. G uidelines on filler m etalsfor use w ith austenitic stainless steels are given

in Table 33 , and for ferritic and duplex stainlesssteels in Table 34 . A dditional sp ecial

requirem ents for w elding of the three fam ilies ofhigh-perform ance stainless steels are

discussed below .

AUSTENITIC STAINLESSSTEEL GRADES

The high-perform ance austen itic stainlesssteels are successfully w elded if the follow ing

issues are addressed:

1. susceptibility to hot cracking2. effect of carbon and oxygen contam ination

on co rrosion resistance

3. m icrosegregation in the fusion zone4. avoidance of interm etallic precipitation in

the H A Z

5. precipitation of chrom ium carbides andnitrides in the heat-affected zones,

sensitization or susceptibility tointergranular attack.

Techniques have b een develop ed to deal w iththese issues; so these grad es are readily

w eldable using all conventional stainless steelprocesses und er all cond itions encountered in

the fabrication shop and the field.

M any of these grades solidify w ith a fullyaustenitic structure; therefore, delta ferrite is not

available to ab sorb im purities and avoid hot

cracking as it is in the standard grad es. The

high-perform ance austenitic grad es behave likenickel-base alloys w ith reg ard to hot cracking;so techn iques used w ith nickel-base alloys

to avoid this problem also ap ply here.C ontam inants that are know n to cause hot

cracking , such as sulphur, phospho rus, oxygen,copper, and zinc, m ust be rigorously excluded

from the w eld zone. This is accom plished byscrupulous cleaning of the w eld area to a

distance several centim etres (one inch) from the



Table 33 Filler metals for welding austenitic stainless steels

Alloy UNS AWS Consumable SupplierClass Number Designation Type C Si Mn Cr Ni Mo N Other Designations

A-1 N08020 ER320LR wire 0.015 0.2 2.0 20 34 2.5 – Cu – A-1 N08825 ERNiFeCr-1 wire – – – 21 42 3 – Cu, Ti 65

A-1 N06625 ERNiCrMo-3 wire 0.015 – – 21.5 61 9 – Cb, Ta 625

A-1 W88022 E320LR coated electrode 0.020 0.2 2.0 20 34 2.5 – Cu – A-1 – ERNiFeCr-1 coated electrode – – – 21 42 3 – Cu,Ti –

A-1 W86112 ENiCrMo-3 coated electrode 0.020 – 0.3 21.5 61 9 – Cb, Ta 112

A-2 S31783 ER317L wire 0.015 0.5 1.7 19.5 14 3.5 – – – A-2 W31713 E317L coated electrode 0.020 0.5 1.5 19.5 13 3.5 – – – A-2 W31735/7 E317LT flux core 0.020 0.5 1.5 19.5 13 3.5 – – – A-2 – – coated electrode 0.020 0.8 1.5 18.5 17.5 4.5 0.15 – SLR-NF A-2 S30986 ER309LMo wire 0.015 0.5 1.8 24 13 2.5 – – – A-2 W30923 E309MoL coated electrode 0.020 0.5 1.5 23.5 13 2.5 – – – A-2 W30938 E309LMoT flux core 0.020 0.5 1.5 23 14 2.5 – – – A-2 W30936 309LNiMoT flux core 0.020 0.5 1.5 22 16 3 – – –

A-3 N08904 ER385 wire 0.013 0.3 1.8 20.5 25 4.7 – Cu 904L A-3 W88904 E385 coated electrode 0.015 0.4 1.8 20.5 25 4.7 – Cu 904L

A-3 N08028 ER383 wire 0.013 0.3 1.8 27.5 32 3.7 – Cu 28 A-3 W88028 E383 coated electrode 0.015 0.5 1.5 27.8 32 3.7 – Cu 28

A-3 N06625 ERNiCrMo-3 wire 0.015 – – 21.5 61 9 – Cb, Ta 625, P12

A-3 W86112 ENiCrMo-3 coated electrode 0.020 – 0.3 21.5 61 9 – Cb, Ta 112, P12

A-4 N06625 ERNiCrMo-3 wire 0.015 0.3 0.2 21.5 61 9 – Cb, Ta 625, P12

A-4 N10276 ERNiCrMo-4 wire 0.015 0.1 0.4 15.5 63 16 – W C276

A-4 N06022 ERNiCrMo-10 wire 0.015 0.1 0.5 21.8 62 13.5 – W C-22

A-4 W86112 ENiCrMo-3 coated electrode 0.020 0.5 0.3 21.5 61 9 – Cb, Ta 112, P12

A-4 W80276 ENiCrMo-4 coated electrode 0.015 0.1 0.5 15.5 63 16 – W C276

A-4 W86022 ENiCrMo-10 coated electrode 0.015 0.1 0.5 21.3 – 13.5 – W C-22

A-6 – – wire 0.015 0.1 0.4 23 60 16 – – P16

A-6 – – coated electrode 0.020 0.3 0.7 25 60 14 – – P16

Table 34 Filler metals for welding ferritic and duplex stainless steels

Alloy UNS AWS Consumable Supplier

Class Number Designation Type C Si Mn Cr Ni Mo N Other DesignationsFERRITIC STAINLESS STEELS

F-1 S44687 ER446LMo wire 0.015 0.3 0.3 26.7 – 1.2 – Nb –DUPLEX STAINLESS STEELS

D-1 S32304 – wire 0.020 0.4 1.5 23 7 – 0.14 – 2304D-1 – – coated electrode 0.030 0.9 0.5 25 9 – 0.12 – 2304D-2 S39209 ER2209 wire 0.015 0.5 1.3 22.5 8.5 3 0.14 – 2205D-2 W39209 E2209 coated electrode 0.020 0.5 1.3 22.5 9.5 3 0.12 – 2205–PWD-2 W39239 W2209T flux core 0.020 0.5 1.5 22.5 9.5 3.3 0.14 – FCW 2205D-3 S39553 ER2553 wire 0.020 0.5 0.8 25.5 5.5 3.4 0.17 Cu –D-3 W39553 E2553 coated electrode 0.030 0.5 1.0 25.5 7.5 3.4 0.17 Cu –D-3 W39533 E2553T flux core 0.020 0.4 1.0 25.5 9.5 3.4 0.15 Cu –D-4 S32750 – wire 0.020 0.3 0.4 25 9.5 4 0.25 – 2507/P100D-4 – – coated electrode 0.030 0.5 0.7 25 10 4 0.25 – 2507/P100



joint. In addition, heat input m ust be m inim ized

by techn iques such as w eld beads em ployingno w eaving and a low interpass tem perature.

Joint designs that m inim ize stresses should beused w herever possible.

C orrosion resistance is red uced if w elds are

contam inated w ith carbon or if the surface is

oxidized in the w eld or heat-affected zone.C areful pre-w eld cleaning and sub seq uent

avoidance of co ntam ination is essential. G astungsten arc (G TA ) w elding an d carefully

designed , non-co pper alloy backing bars arerecom m end ed for good inert gas coverage

of root passes w here the backside is not

accessible. A gas diffuser screen should be

used to m inim ize turbulence in the G TAshielding gas. S trong drafts should be avoided

during w elding to m inim ize air en trainm en t inshielding atm ospheres. A ll starts and stops

should be g roun d out before continu ingw elding , and all slag should be rem oved

betw een passes w hen using co ated

electrodes or w elding processes inco rporatingfluxes. The o ptim um co rrosion resistan ce is

restored w hen the w eld heat tint is rem oved ;and, in critical applications, it is im perative

that tint is rem oved.

The austenitic stainless steels are prone to

chrom ium and

m olybdenum m icro-segregation w ithin the

w eld m etal. This red ucesw eld m etal co rrosion

resistance to lessthan that of the base

m etal w hen w elding

autogenously or w ithm atching filler m etal. This

effect becom es m oresevere as the alloying

The world’s first paper

continuous digester

built entirely of 2205

duplex stainless steel



co ntent, esp ecially m olybdenum , increases.

The resultant reduction in pitting resistance ina ferric chloride environm ent is illustrated in

Figure 70 . The effect also beco m es m oresevere as section size and heat input increase,

and the loss in co rrosion resistance is enoughto req uire that the w elding consum ab le be

m ore h ighly alloyed than the base m etal. O ver

alloying in the filler is intended to give w eldm etal co rrosion resistance that m atches that

of the base m etal. M any of the fillers d esignedfor the m ost highly alloyed stainless steels in

sub groups A -4 and A -6 are m od ifications ofcorrosion resistant nickel-base alloys. In

addition to the w eld m etal itself, the unm ixedfusion zone m ay be susceptible to this sam e

m icro-segregation effect. U sing sufficient heatinp ut to ensure m axim um w eld poo l m ixing

m ay m inim ize this.

C arbide and nitride sensitization, and loss o f

corrosion resistan ce from hea t-affec ted zone

interm etallic phase precipitation, are possible

occurren ces that m ay result from exc essiveheat inp ut or inad eq uate co oling rates. H ea t

inputs are generally lim ited to less thanab out 16 kJ/m m (400 kJ/inch), but sho uld

still be high en ough to p rovide fusion zonem ixing. Interpass tem perature lim its of

100°C (212°F) help en sure rap id co oling

rates betw een passes.

The g oal behind the p rinciples of joint designand w elding practice for the austenitic stainless

steels is avoidance of excessive heat input andexcessive dilution from the base m etal, w hile

ensuring com plete penetration and freedomfrom oxidation and slag . This req uires generous

groove ang les and gap w idths, w ell-designedbacking bars, and the use of diffuser screens.

Tack and string er bead starts and stops shouldbe g round ou t and all w eld slag rem oved

before subseq uent passes w hen using coated

electrodes or w elding processes involving

fluxes. The finished w eld

sho uld be thoroug hlycleaned of all sp atter and

oxide as d iscussed in the“S urface C ondition”

section.

Figure 70 Effect of welding and molybdenumcontent on weld corrosion resistanceof austenitic stainless steels whenwelded by the GTA process without filler metal 66

1 2 3 4 5 6 7

C r i t i c a l P

i t t i n g T e m p e r a t u r e

i n 6 %

F e C I 3 ( ˚ C ) C

r i t i c al P i t t i n gT em

p er a t ur ei n

6 % F e CI 3

( ˚ F )

Molybdenum (wt. %)

Unwelded

Welded

908580757065605550454035302520151050

-5

194185176167158149140131122113104958677685950413223



FERRITIC STAINLESSSTEEL GRADES

The ferritic stainless steels are perhaps

the m ost com plex from the standpoint ofw eldab ility and are seldom w elded in anything

but thin sections b ecause of their toughnesslim itations. These grad es w ill be discussed only

in term s of tub e-to-tub esheet w elding and thew elding of thin sheet. In all cases, thorough

deg com plexasing is m andatory to avoid carburizationof the w eld and heat-affected zone. Very good

inert argon or helium shielding and backing gas



co ndition generally have m ore than theoptim al am ount of ferrite. P ost-w eld

annealing co nverts som e o f the hightem perature ferrite produced by w elding back

to austenite. A nnealing conditions for thesew eldm ents, including the need for rap id

co oling, follow the sam e principles as

discussed previously for base m etal.

W hen post-w eld annealing is not em ployed,a filler m etal over-balanced w ith austenite

form ers is usually used. This p rovides therequired austenite-ferrite balance in the high

tem perature reg im e just below the solidustem perature, and this balance is retained in the

w eld m etal by the relatively fast cooling ratesassociated w ith w elding. The therm al cycle is

designed to p rom ote the reversion o f the heat-affected zone (H A Z) from ferrite to austenite. A

rap idly cooled , single-pass w eld m ay have asm uch as 90% ferrite in the H A Z. The optim um

therm al cycle acco unts for section thickness

and the num ber of passes to allow foradequate reversion of this ferrite back to

austen ite. In thin sections w ith few passesand at cold am bient tem peratures, som e

preheating and relatively high heat input m aybe necessary to assist w ith adeq uate w eld

annealing of the prior passes. A s section size

and the num ber of passes increase, the needfor preheat and high heat input dim inishesuntil the o ther extrem e is reached. Interpass

tem perature lim its are im posed to m inim izenitride, carbide, sigm a, and alpha prim e

precipitation resulting from the cum ulative heat

input of m any passes. The effect of heat inputon optim izing corrosion resistance for 2205

stainless steel is illustrated in Figure 72 . Thedetrim ental effect of high heat inp ut becom es

larger w ith the m ore highly alloyed grad esbecause of their m ore rap id interm etallic phase

precipitation kinetics.

O xidation of the w eld m etal has an ad verseeffect on corrosion resistance and m echanical

properties. This is esp ecially im portant inw elding processes that use fluxes for w eld

protection. Increasing w eld m etal oxygen

content reduces the critical pitting tem perature

as show n in Figure 73 for both dup lex andaustenitic w elds. Toughness is a lso red ucedsignificantly in the duplex g rades w ith w elding

processes that im part high o xygen or slagco ntent. This is show n in Figure 74 , w here the

subm erged arc w eld w ith rutile flux, know n fordelivering high oxygen w eld m etal, is inferior

to the other w elding processes. Toughnessincreases w ith processes capab le o f

m aintaining g ood w eld m etal purity.

Figure 71 Effect of shielding gas nitrogencontent on the weld pitting

resistance of S32760 high- performance duplex stainless steel 67

0.1 0.2 0.3 0.4 0.5 0.6

C r i t i c a l P


i n 6 %

F e C I 3 ( ˚ C )

Nitrogen in Weld Root (%)

66

64

62

60

58

56

54

52

50

ArAr+2%NAr+3%NAr+5%N

Figure 72 Effect of weld arc energy onthe weld corrosion resistanceof 2205 duplex stainless steel evaluated in 6% ferric chloride 68

0 1 2 3 4 5 6 7

C o r r o s i o n

R a t e

( g / m 2 / h r )

Heat Input (kJ/mm)

1.00

0.10

0.01



S om e principles of joint design and w eldingpractice are of special im portance to thedup lex g rad es. The joint geom etry should be

w ide enough to easily allow full penetration.A rc strikes should be m ade w ithin the joint.

C onsideration should be given to G TA w eldingfor the root pass if the root is exp osed to the

critical environm ent. A deq uate backing andshielding gas should be available and the

w elder sho uld be able to observe the w eld

pool and any slag form ation. Excessivew eaving should be avoided to p revent

excessive heat inp ut and conseq uentinterm etallic phase form ation, and extrem ely

low heat inp ut sho uld be avoided to preventferrite-rich heat-affected zones. A n excellent

discussion on the w elding of duplex stainlesssteels is p rovided in the N iD I reprint

N o. 14 03 6, “W elding D up lex and S up er-D uplex S tainless S teels”.

Figure 73 Effect of backing gas oxygen content on the weld corrosion of 904L austenitic and 2205 duplex stainless

steels evaluated in 3% NaCl at 300 mV, SCE 69

C r i t i c a l P

i t t i n g T e m p e r a t u r e ( ˚ C

) Cr i t i c al P i t t i n gT em

p er a t ur e ( ˚ F )

100

90

80

70

60

50

40

30

20

10

0

212

194

176

158

140

122

104

86

68

50

32Parent Ar+<5ppm 02 Ar+50ppm 02 Ar+150ppm 02 N2+10% H2Ar+25ppm 02

2205

904L

Figure 74 Effect of weld practice on thetoughness of 2205 duplex

stainless steel weld metal 70

˚F -94 -76 -58 -40 -22 -4 14 32˚C -70 -60 -50 -40 -30 -20 -10 0 10

I m p a c t

E n e r g y

( j o u l e s ) I m

p a c t E n

e r g

y ( f t .- l b s . )

Temperature

120

100

80

60

40

20

0

88

74

59

44

29

15

0

GTAW

GMAW

Rutile SMAW RutileSAW

Basic SAW

Basic SMAW



SURFACECONDITION

Tw o im portant considerations in the use of the

high-perform ance stainless steels are the needto avo id surface contam ination and to provide

for clean surfaces both during fab rication and

service. B oth m ust be co nsidered w henplanning the fabrication of stainless steeleq uipm ent. A ny h igh tem perature o peration

m ust avo id the introduction of carbon andsulphur into the surface. The surface m ust be

free of any detrim ental co ntam inan ts beforeannealing or w elding , and the atm osphere itself

m ust not introduce contam inants. S urfaceoxide o r heat tint produced during w elding is

undoub ted ly the m ost frequently encountered

co nd ition that can lead to co rrosion problem s.W hile detrim ental to all stainless steels,

unrem oved surface oxide is especially harm fulto the high-perform ance stainless steels

because the surface oxide is accom panied byunderlying chrom ium dep letion. B ecause

co rrosion resistance dep ends strongly on the

chrom ium content, any low ering of chrom iumat the surface red uces corrosion resistance.

The chrom ium dep letion, if no t rem oved , is alikely source of corrosion initiation in the severe

environm ents in w hich the high-perform ancestainless steels are typ ically used.

It is not sufficient to m erely specify “slag,

oxide, and heat tint rem oval”follow ing w eldingop erations because the m ethod of rem oval

m ay strongly influence the ultim ate corrosion

resistance of the m aterial. S om e rem ovalm etho ds generate heat or leave d isturbed

m etal that is still not in an ideal condition toresist co rrosion. A num ber of studies have

exam ined the effectiveness of various oxiderem oval m etho ds; an exam ple o f typical results

is provided in Figure 75 . A cid pickling, either by

im m ersion or w ith pickling paste, is the m osteffective m ethod; it w ill rem ove the chrom ium -dep leted layer as w ell as the surface o xide.

S pecially form ulated, strong pickling acidsare req uired because of the high corrosion

resistance of the h igh perform ance stainless

steels. O n the otherhand, coarse grit

grinding has little benefitand has been show n

to be detrim ental insom e cases. The heat

generated by coarsegrit grinding can easily

produce heat tint on theground surface w hich

then recreates theinitial condition. N iD I

pub lications N o. 10 004,

“Fabrication and P ost-Fab rication C leanup o f

S tainless S teels”andN o. 10 068, “S pecifying

S tainless S teel S urface

Treatm ent”, provideexcellent discussionson all asp ects o f this

im portant topic.

Figure 75 Effect of post weld surface cleaning methodson the corrosion resistanceof 2205 and 904L stainless steel welds

AsWelded

PickleBath

Grind360 Grit

BrushStainless

Steel

Brush3M

BlastPicklePaste

C r i t i c a l P


( ˚ C

i n 3 %

N a C

I , + 3 0 0 m

V S C E )

80

70

60

50

40

30

20

10

0Grind

80 Grit

2205

904L



APPLICATIONS

The high-perform ance stainless steels

collectively o ffer a great variety in m echanical,physical, m etallurgical, and corrosion

prop erties, w ith the com m on them e b eing thatthey are very resistant to strong chloride and

oxidizing to red ucing acid environm ents. Thus,the applications in w hich they are used are

extrem ely varied and usually m uch m orecorrosive than w ould be suitable for the

standard stainless steel grad es. The h igh-

perform ance stainless steels are b eing used inliterally thousands of different applications in

m any areas of the process, energy, paper,transp ortation, and other industries. They are

available in essentially all product form s andare covered by m any industry specifications.

To assist the designer w ith grad e selection, a

sum m ary of the stainless steel subgroups interm s of their general characteristics and areas

of application is p rovided in Table 35 . Theillustrations o f applications used throughout this

book are o nly a sm all sam pling of this w ideexperience and show som e of the unique

and dem anding applications w here h igh

perform ance stainless steels are successfullyused . In so m e cases, the application m ight be

based on extending the service life o ver w hatm ight be obtained w ith Type 316 stainless

steel; in other cases, it m ay represent a uniqueneed that can only be filled by one o f these

truly rem arkable grad es. The high-perform ancestainless steels provide a cost-effective so lution

to m any dem and ing application prob lem s.

Heat exchanger with

SAF 2507 ® tubes

for aggressive

chloride service



Table 35 Representative corrosion characteristics and applicationsfor high-performance stainless steels

Alloy Group PRE Number Description Applications

AUSTENITIC ALLOYS A-1

A-2

A-3

A-4

A-5

A-6

D-1

D-2

D-3

D-4

F-1

F-4

26-28

30-32

32-36

40-43

29-41

45-54

27

34-40

22

30-34

32-39

36-38

Resistant to mid-concentration sulphuric and other strong, mild-ly reducing or oxidizing acids. Resistant to stress corrosion andpitting (at high PRE number)

Good resistance to mildly acidic, moderate chloride aqueousenvironments while providing a moderate strength advantage

Good general and stress corrosion resistance in strong acidsat moderate temperatures and in organic acids at hightemperatures

Very good chloride pitting and stress corrosion resistance;resists seawater and many saline acidic waters, and manyacids and caustics; provides a substantial strength advantage

Very high strength and good general corrosion and pittingresistance

Very high strength with excellent chloride pitting and stresscorrosion resistance, resists warm seawater and high chloride,acidic and oxidizing waters and brines; excellent resistance toa wide variety of acids and caustics

Excellent chloride stress corrosion cracking resistance with

good resistance to pitting; excellent resistance to hot organicacids and caustics

Resistant to pitting and crevice corrosion in ambienttemperature seawater; good stress corrosion resistance inhigh temperature water; good strength

Good stress corrosion resistance in cooling waters and underevaporative conditions; high strength

Good pitting and stress corrosion resistance; good resistance tooxidizing acids and caustics; high strength

Very good pitting and stress corrosion resistance, goodresistance to mildly reducing and oxidizing acids and caustics;high strength

Resistant to seawater pitting and crevice corrosion; very goodstress corrosion resistance; good resistance to mildly reducingacids and oxidizing acids and caustics; high strength

Heat exchanger tubing handling fresh water, organic acid

condensers, caustic evaporator tubing

Seawater-cooled condenser tubing; heat exchanger tubinghandling fresh and brackish water and organic acids

Equipment handling water, foods, and pharmaceuticalswhere better strength or stress corrosion resistance isneeded compared to Type 304

Pressure vessels, piping,pumps and valves where strength andweight are factors along with resistance to stress corrosionand fatigue; general purpose heat exchanger tubing

Where better pitting and crevice corrosion resistance isneeded compared to the D-2 alloys

Pumps, valves, and high pressure piping and pressuretubing handling seawater or chloride containing waters

FERRITIC ALLOYS

DUPLEX ALLOYS

Process equipment handling sulphuric acid solutions;condensers and coolers handling acid-chloridecondensates where stress corrosion is a problem

FGD absorbers and piping operating under mild conditionspaper bleach equipment requiring improved performancecompared to Type 316

General process equipment

Process equipment for all but strong reducing and hotsulphuric acids; piping and heat exchangers handlingambient seawater; FGD absorbers and paper bleachequipment operating at moderate Cl-pH-T conditions

Where high strength is important

Process equipment for all but strong reducing and hotsulphuric acids; piping and heat exchangers/evaporatorshandling hot seawater and brines; FGD absorbers andpiping operating at high chloride levels; highly oxidizingpaper bleach applications



The autho r w ould like to thank D r. Jam es D .R edm ond and D r. R alph M . D avison for their

m any contributions to the co ntent of thisdocum ent, D r. M ichael A . S treicher, B ill M olloy,

and M .J. S chofield for their careful criticism ,

and the N ickel D evelopm ent Institute for itssupport. The author also w ishes to

acknow ledge all of tho se engineers andscien tists w ho w ere responsible for the creation

of this rem arkable fam ily of stainless steels.

1. M etals H andbook, 8th Edition, 1973, Am erican S ociety for M etals, M etals P ark, O hio, pp. 425, 291

2. Ettw ig, H . H . and P epperhoff, W ., A rch. Eisenhüttenw esen, Vo l. 41, 1970, p. 471

3. Lula, R .A ., ed ., S ource B ook o n the Ferritic S tainless S teels, A m erican S ociety for M etals,M etals P ark, O hio, 1982

4. P ugh, J. W . and N isbet, J.O ., Transactions A IM E, Vo l. 18 8, 1950, p. 2735. P eckner, D . and B ernstein, I. M ., H and boo k of S tainless S teels, M cG raw -H ill B ook C om pany,

N ew York, 1977 , p. 12-136. W eiss, B . and S tickler, R ., M etallurgical Transactions, Vol. 3, 1972, p. 851

7. Thier, H . A ., B am m el, A. and Schm idtm ann, E., Arch. Eisenhüttenw esen, Vol. 40 N o. 4, 1969, p. 3338. Q varfort, K ., “Intergranular C orrosion Testing by E tching at a C onstant P otential”, C orrosion,

Vol. 51 N o. 6, June 1995, pp. 46 3-468

9. D em o, J.J., “S tructure, C onstitution, and G eneral C haracteristics of W rought Ferritic S tainlessS teels”, S .T.P. 619, A S TM , W est C onshohocken, P ennsylvania, 1977

10. B row n, E.L., et. al., “Interm etallic P hase Form ation in 25C r-3M o-4N i Ferritic S tainless S teel”,M etallurgical Transactions A , Vo l. 14A , M ay 1983, p. 791

11. K ovach, C . W ., Eckenrod, J. J., and P innow , K . E., “W elded Ferritic S tainless S teel Tubing forFeedw ater H eaters”, R eprint N o. 85 -JP G C -40 , A S M E, N ew York, 19 85

12. N ichol, T. J., D atta, A ., and A ggen, G ., “Em brittlem ent of Ferritic S tainless S teels”,M etallurgical Transactions A , Vol. 11A , A pril 1980, p. 573

13. Josefsson, B ., N ilsson, J-O ., and W ilson, A ., “P hase Transform ations in D uplex S teels and theR elation B etw een C ontinuous C ooling and Isotherm al H eat Treatm ent”, P roceed ing s, D up lex

S tainless S teels ’91, O ctober 28-30, 1991, B ourgogne, France, p. 6714. H oung lu, C . and H ertzm an, S ., “K inetics of Interm etallic P hase Form ation in D uplex S tainless

S teels and Their Influence on C orrosion R esistance”, IM -2689, S w ed ish Institute for M etalR esearch, S tockholm , S w eden

15. H erbsleb , G . and S chw aab, P., P recipitation of Interm etallic C om pounds, N itrides and

C arbides in A F 2 2 D uplex S teel and Their Influence on C orrosion B ehavior in A cids,P roceed ings, D up lex S tainless S teels, A S M , S t. Lo uis, M issouri, 1983, p. 15

16. Iturgoyen, L. and A nglada, M ., “The Influence o f A ging at 475°C on the Fatigue C rackP ropagation of a D uplex S tainless S teel”, P roceedings, Stainless S teels ’91 International

C onference on S tainless S teels, C hiba, Jap an, 1991

ACKNOWLEDGEMENTS

WORKS CITED



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of S eaw ater-C oo led P ow er P lant C ondensers O perating w ith H igh-P erform ance

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C anada, 199266. G arner, A ., “C orrosion o f H igh A lloy A usten itic S tainless S teel W eldm ents in O xidizing

Environm ents”, M aterials P erform ance, Vol. 21, A ugust, 1982, p. 967. W arburton, G . R ., S pence, M . A ., and H ealiss, T., “The Effect of W elding G as

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C orrosion R esistance”, M aterials S election and D esign, M arch, 1985, p. 5869. O degard, L. and Fager, S . A ., “The R oot Side P itting R esistance of S tainless Steel

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W elding A nnual A ssem bly, The H ague, The N etherland s, 19 9171. O deg ard, L. and Fager, S . A ., “The R oot S ide P itting R esistance of S tainless S teel

W elds”, S andvik S teel W elding R ep orter, Vol. 1, S andvik S teel, 1990



The follow ing p ublications can be obtained from :

N ickel D evelopm ent Institute

214 K ing S treet W est, S uite 510Toronto, O ntario M 5H 3S 6

C anadaP hone: 416-591-799 9

Fax: 416-591-7987w w w .nidi.org

428 Fabrication of C hrom ium -N ickel

S tainless S teel (300 series)

10 0 02 Evaluating Installed C ost ofC orrosion-R esistan t Piping

10 004 Fabrication and P ost-FabricationC leanup of S tainless S teels

10 006 H igh-Perform ance A ustenitic

S tainless S teels in the P ulpIndustry

10 017 S tainless S teel Is C ost-Equivalentto FR P for U se in the B leach P lant

10 023 Life C ycle C ost C om parison of

A lternative A lloys for FG DC om ponents

10 0 24 The U se of N ickel S tainless Steels

and N ickel A lloys in Flue G asD esulphurization S ystem s in the

U nited S tates

10 025 Flue G as D esulphurization; theEuropean S cene

10 032 Practical G uide to U sing 6M o

A ustenitic S tainless S teel

10 039 S tainless S teel S heet Lining of

S teel Tanks and P ressure Vessels

10 043 D esign, W ater Factors Affect

S ervice-W ater Piping M aterials

10 044 Practical G uide to U sing D uplexS tainless S teel

10 06 8 S pecifying S tainless S teel S urface

Treatm ents

11 003 G uidelines for S election o f N ickelS tainless S teels for M arine

Environm ents, N atural W aters andB rines

11 007 G uidelines for the W eldedFabrication o f N ickel-C ontaining

S tainless S teels for C orrosion-R esistan t S ervices

11 008 M achining N ickel A lloys

12 001 Life C ycle C ost B enefits of

C onstructing an FG D S ystem w ith

S elected S tainless S teels andN ickel-B ase A lloys

12 002 P erform ance of Tubular A lloy H eat

Exchanges in S eaw ater S ervice inthe C hem ical P rocess Industries

13 007 Flue G as D esulphurization in Japan

14 013 C orrosion of M etallic and

N onm etallic P iping for B leach P lantD S tage Filtrate

14 014 P erform ance of H ighly-A lloyed

M aterials in C hlorine D ioxideB leaching

14 020 W eld Fabrication of a 6%M olybd enum A lloy to A void

C orrosion in B leach P lan t S ervice.

APPENDIX 1 ADDITIONAL READING



14 023 Perform ance of H ighly Alloyed

M aterials in C hlorination B leaching

14 026 C orrosion B ehaviour of S tainless

S teel, N ickel-B ase A lloy andTitanium W eldm ents in C hlorination

and C hlorine D ioxide B leaching

14 029 Fabrication O ptions for N ickelC ontaining A lloys in FG D S ervice:

G uidelines for U sers

14 036 W elding D uplex and S uper-D uplexS tainless S teels

15 001 N uclear S ervice W ater P iping

15 002 N uclear S ervice W ater P iping

The follow ing p ublications can b e obtained from :

N A C E International

PO B ox 218340H ouston, Texas 77218

U .S .A .P hone: 713-492-0535

Fax: 713-492-8254

1. N AC E S tandard R P0292-92.Installation of Thin M etallic

W allpaper Lining in A ir P ollutionC ontrol and O ther P rocess

Eq uipm ent

2. N AC E Standard M R 0175. Sulfide

S tress C racking R esistan t M etallicM aterials for O ilfield Equipm ent

3. N AC E Report 1F192. U se of

C orrosion R esistant A lloys inO ilfield Environm ents (1993

R evision)

ADDITIONAL READING (continued)



AUSTENITIC HIGH-PERFORMANCE STAINLESS STEEL PRODUCER NAMES

Name UNS Number Class Producer Names Alloy 20 N08020 Carpenter 20Cb-3, Nicrofer 3620 Cb,VLX 920, DMV 920, AL 20,

INCO alloy 020, NAR-20-3, Sumitomo HR10, NTK 30A, NTK 30A A-1

Alloy 825 N08825 INCOLOY alloy 825,AL 825, Sandvik Sanicro 41, L 314, UR 825 VLX 825, DMV 825, Nicrofer 4221, NAR-825, Sumitomo HR11

317LN S31753 CLI 168 HE, YUS 317LN260 YUS 260, R 315CX

A-2317LM S31725 CLI 68 BC, NTK M5317LMN S31726 Cronifer 1713 LCN, Sandvik 3R68,

CLI 170 HE, NIROSTA 4439204X NAS 204X310MoLN S31050 Sandvik 2RE69, Sumitomo HR3 ELM700 N08700 JS 700904L N08904 URANUS B6, Sandvik 2RK65, AL 904L, NAR-20-25LMCu

VLX 904L, DMV 904L, Cronifer 1925 LCN, POLARIT 774,Sumitomo HR8C,Avesta Sheffield 904L

A-3904LN URB6N, NIROSTA 4539

20Mo-4 N08024 20Mo-420 Mod N08320 NAR-20-25MTI, Sumitomo HR8

Alloy 28 N08028 Sandvik Sanicro 28,VEW A958,A958, VLX 928, DMV 928,Nicrofer 3127 LC, URANUS B28, Sumitomo HR21

20Mo-6 N08026 Carpenter 20Mo-625-6MO1925 hMo N08925 / N08926 INCO alloy 25-6MO, NAR-AC-3, NTK M6, NAR-AC-3,

Sumitomo HR8N, Cronifer 1925 hMo, URANUS B26, NTK M6254N NAS 254N

A-4SB8 N08932 URANUS SB8254 SMO S31254 Avesta Sheffield 254 SMO, Sandvik 254 SMO, Sumitomo HR254,

POLARIT 778, YUS 270, VLX 954, DMV 954, VEW A965, A965 AL-6XN N08367 AL-6XN YUS 170 YUS 170

2419 MoN A-5 Cronifer 2419 MoN4565SS34565 NIROSTA 4565SB66 S31266 URANUS B663127 hMo N08031 A-6 Nicrofer 3127 hMo654 SMO S32654 Avesta Sheffield 654 SMO

APPENDIX 2 (A)

APPENDIX 2 (B)FERRITIC HIGH-PERFORMANCE STAINLESS STEEL PRODUCER NAMES

Name UNS Number Class Producer Names26-1S S44626 26-1S, Sumitomo FS3Ti, R24-2

F - 1E-BRITE 26-1 S44627 E-BRITE 26-1, R26-1MONIT S44635 MONIT

F - 2SEA-CURE S44660 SEA-CURE

AL 29-4C S44735 AL 29-4C, NTK U-20 AL 29-4-2 S44800 F - 3 AL 29-4-2, Sumitomo FS10



ACCEAIERIE DI BOLZANOAB 318, AB 327 U , AB 327

ACCEAIERIE VALBRUNA V225M N , V257M W U , V257M

ATI PROPERTIES, INC.A L 825, A L 904L , A L-6X N ®, JS 700 ®,

AL 20

E-B R ITE 26-1 ®, A L 29-4C ®, A L 29 -4-2 ®

AL 255 , A L 2205

AVESTA SHEFFIELD ABAvesta S heffield 25 4 S M O ®, Avesta

S heffield 65 4 S M O ®, Avesta S heffield

904LM O N IT®

Avesta S heffield 2205, Avesta S heffield2205 C ode P lus Tw o ®, A vesta

S heffield S A F 2 507 ®, Avesta Sheffield2304 , Avesta S heffield 44LN

BÖHLER EDELSTAHL GmbHA 958, A 965 , L 31 4

A 903, A 911

CARPENTER TECHNOLOGY CORPORATION

20C b-3 ®, 20M o-4 ®, 20M o-6 ®

7-M o PLUS®

COGNE ACCIAI SPECIALI329 A , 329 S , 329 S /1

CREUSOT-LOIRE INDUSTRIEU R A N U S® SB 8, UR AN US® B26,

U R A N U S® B66, U RA N U S® B28,U R A N U S® B 6

C LI-68B C , U R 825, U R B 6N , C LI S A F2507, C LI 170 H E ®, C LI 168 H E ®

U R A N U S® 35N , UR AN US® 45N,

U R A N U S® 4 5N M o , U R A N U S® 45N+,U R A N U S® 47N , U RAN U S® 52N,

U R A N U S® 52N +, U RAN U S® 76N

CRUCIBLE MATERIALS CORPORATION26-1S, SE A -C U R E ®

DMV STAINLESSD M V® 825, D M V® 904L, D M V® 920,

D M V® 928, D M V® 954

D M V® 22-5, D M V ® 25-7, D M V ® 25-7N ,D M V® 25-7C u, D M V ® 25-7N C u

KAWASAKI STEEL CORPORATIONR 315 C XR 24-2, R 26-1

KRUPP THYSSEN NIROSTA GmbHN IR O STA® 4439, N IR O S TA ® 4539,

N IR O STA® 4565SN IR O STA® 4462, N IR O S TA ® 4501

KRUPP VDMN icrofer ® 3620 C b, N icrofer ® 4221,

C ronifer ® 1713 LC N ,

C ronifer ® 1925 hM oC ronifer ® 1925 LC N , N icrofer ® 3127LC ,

C ronifer ® 2419 M oN ,

N icrofer ® 3127 hM o

MEIGHS LIMITEDFER R ALIU M® alloy 255

NIPPON METAL INDUSTRY CO. LTD.N TK 30A, N TK 30AC , N TK M 5,

N TK M 6

N TK R -5, N TK R -8N TK U -20

NIPPON YAKIN KOGYO CO. LTD.N AS 204X, N AS 254NN AS 64, N AS 45M

OUTOKUMPU POLARIT Oy P olarit 777, P olarit 778, VEW A 958,

V EW A 965

APPENDIX 4PRODUCER-REGISTERED TRADEMARKS AND TRADE NAMES



SANDVIK ABS andvik S anicro 4 1, S andvik 2R E69 ,

S andvik 2R K 65 , S and vik S anicro 28,

S andvik 254 SM OS andvik SA F 230 4 ®, S and vik S A F

2205 ®, S andvik S A F 2507 ®,S andvik 3R 68

SPECIAL METALS CORPORATIONIN C O LOY® alloy 825

SUMITOMO METAL INDUSTRIES, LTD.YU S 317LN , YU S 170, YU S 260, YU S

270 , YU S D X1, N A R -825, N A R -20-3,

N AR -AC -3,N A R -20-25M TI, N A R -20-25LM C u,

Sum itom o H R 3 ELM , Sum itom o H R 8,Sum itom o H R 8C , Sum itom o H R 8N ,

Sum itom o H R 10, S um itom o H R 11,Sum itom o H R 21, Sum itom o H R 254

FS3Ti

N AR -D P3, N AR -D P3W , N AR -D P8,

SUMITOMO METAL TECHNOLOGY, INC.S um itom o FS10

Sum itom o D P3W

TRAFILERIE BEDINI

4462

UGINE SRL ITALIA 4462, 4507

VALLOUREC MANNESMANN TUBESVM® 22 , VM ® 25

(handbook) high performance stainless steels (11021)

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